Should the UK rejoin the EU?

No.
it has not turned out the way I thought it would, but that is the fault of Tory Governments since Boris

100% no and never again as we would be much worse off over time.

Should the UK rejoin the EU?

No

Why

See above.

While we have yet to see any other states on the brink of leaving, shifts in the political climate in several countries suggest that, sooner or later, the EU will fracture - particularly if it continues on the path of trying to absorb economically weak and politically unstable countries on its fringes.

I don't think anyone has suggested that the EU is perfect or that "all is well". There have always been political and other issues. I don't see how you can realistically avoid them with an organisation of that size. To some degree, as with many of the coalition governments in those individual countries, debate, disagreement and compromise is a necessity and the status quo rather than something to be concerned about.
As for this prediction, the fall of the EU has been predicted by Eurosceptics for pretty much as the project has existed. So many of them very confidently predicted that we would be the first domino to fall when we voted to leave in 2016. Now that that hasn't happened, they've fallen back on vague notions of "well, yeah, but it's still in trouble and will fall apart eventually". It's very easy to be confident in a prediction that can always be pushed back to "at some point in the future", because by definition you can never actually be wrong. In reality, the far more salient point is that people have been making these predictions for over fifty years now and have never been correct.

In response to your first point, I readily accept that there will always be debate, disagreement and compromise among nations, even among close allies. Indeed, I am all in favour of it. However, there are growing tensions in regard to key issues where disagreements could become so great that they may ultimately threaten the EU's existence: notably immigration, climate control and enlargement.

As regards the second point, I was being rather more specific than you make out, referring as I did to the potential accession of a number of economically weak and politically unstable countries, two of which have large populations and all of which would be holding out the begging bowl. This makes it significantly more likely than in the past that one or more of the net contributors to the EU budget may eventually choose to leave.

When talking about the EU, we need to distinguish between the EU of today and its antecedents. Many of those who voted leave in the 2016 referendum would have been among the 67% of the participating UK electorate who voted to remain in the Common Market referendum of 1975. What happened in between was that the nature, purpose and membership of the organisation radically changed along with its nomenclature.

So I reiterate: in the hypothetical circumstances of aspiring to rejoin an EU of 15 members that we almost certainly would never have left in the first place there would be a strong argument in favour. But the idea of rejoining the EU as it is today holds much less merit.

I think that third paragraph is on somewhat shaky territory. I haven't seen any data on the number of voters who changed their vote between 1975 and 2016 in favour of leave. There will have been some I'm sure. Whether there were many depends on your definition. But irrespective, implying that they will have changed their mind because of how the EU itself changed in that time is somewhere between overly simplistic and flat out inaccurate. We both know that the various leave campaigns advanced much more simplistic arguments than that, and whilst there was some mention of how the EU has changed since 1975, I expect only the smallest of minority of leave voters generally would be able to give you any sort of detail as to how it is that it changed. Certainly nowhere near the level of detail that you and I could describe.
I see your point generally, though, and you're entitled to it. I see how you can arrive at the conclusion that this combination of circumstances and events will lead the EU down a path from which significant change will result. I just take the view that recency bias means that we're generally going to see current events as ones that don't have solutions, mainly because we haven't seen them yet. But there have been various major issues and crises over the decades. Many people made the same arguments after the Greek bailout in 2010 that you're making now regarding the economically weaker countries, and that crisis, such as it was, was successfully navigated. I will say at the time it also did feel much more existential in the wake of the 2008 crash than these issues do now. But fundamentally I struggle to see the path from this set of circumstances to the EU breaking apart. That would be a very technical and difficult process, and not something that can happen by accident. Frankly I think the will to keep the EU together, and maintain the status quo one way or the other, is stronger than any will to fracture it.

The question would seem to be based on the assumption that all is well with the EU, when clearly it is not.

The question would seem to be based on the assumption that all is well with the EU, when clearly it is not. Brexit may or may not have been the right decision, but it is done.
Why seek to rejoin an organisation that is riven with internal dissent and with a leadership that is increasingly out of touch with the aspirations of the citizens it purports to represent? While we have yet to see any other states on the brink of leaving, shifts in the political climate in several countries suggest that, sooner or later, the EU will fracture - particularly if it continues on the path of trying to absorb economically weak and politically unstable countries on its fringes.
Rejoining the EU of 15 mainly wealthy and culturally compatible nations that existed prior to the enlargement of May 2004 might be a different matter. But if that version of the EU had still been in existence in 2016 we would almost certainly never have left in the first place.

Sure, there is dissent within the policymaking of the EU, however that's just democracy. The EU is one of the strongest alliances in the world.
Of course the decisions made by the EU can't please everyone, it's an international organisation with 27 countries, but surely the UK having a seat at the table would improve outcomes for us, because we would actually be in it? The argument that it is 'out of touch,' literally proves our point, because if we were in it we would actually have influence over decisions made.
It's obvious the benefits to the economy with it would bring - I don't think that can even be debated.
As outlined by previous posters, this rhetoric the EU will fail is just an excuse to try and prove a point without any actual evidence.
Finally, especially at a time like now - with the huge threat of war from Russia and the US' leadership, surely improved diplomacy and cooperation is imperative?

Hmm, I see you're still struggling with basic concepts. This might help...
Imagine you are on a boat that is overrun with venomous snakes, no supplies, is sinking, and is on fire.
A boat pulls alongside. It has rats in the bilge, only stale bread and Red Bull, a slow leak, and a smokey engine.
Which boat is the better option?

How can you not see his point? Do you really lack the basic comphrehension skills necessary to realise he is likening our current situation with the possibility of joining the EU?