Fireopal,
Firstly, allow me to say that I'm glad this thread came about, because you are educating me about these conditions, which is obviously a very good thing.
Your decription of internal compensatory mechanisms makes sense, and I can see how these could be greatly advantageous in many situations. Where I probably generalised before in saying dyslexia lowers the ability of one of two otherwise similar people, I probably should have said - and it pains me to write this, I don't mean it in a patronising politically correct manner, so take it literally - differently abled. That is, advantaged in some areas (you mentioned long term memory and imagination, for example), and disadvanted in others.
I think that the evaluating the talent set an individual possesses is, maybe unfortunately, going to be influenced by assumptions based on characteristics exhibited by the majority of the population. For example, if two people were given a problem at work and told to come back in two weeks with a solution, maybe a dyslexic person would produce the superior solution in a shorter amount of time. This is based on what you have said regarding compensatory mechanisms. However, if the same two people were told that for every hour it takes them to read a report and form an action plan based on it, £100,000 pounds was being lost, I imagine the non-dyslexic individual would more often than not save more money.
Now of course, there is nothing wrong with any of this, but unfortunately, a person evaluating the two individuals is most likely not going to take into account the possibility of such differences. I think that they should be able to take such differences into account, (and in the examples above, this could result in selection of either candidate, depending on the selection criteria).
You stated that "People with learning differences can be trusted to recognise their strengths and weaknesses". Of course this is true. But to my mind, it generalises slightly and implies the obvious untruth that all people with learning differences can be trusted to recognise their strengths and weaknesses.
Of course, not all people without learning differences (surely we all have learning differences! But I digress...) can be trusted to recognise their strengths and weaknesses either, this is not specific to any one group of the population. Moreover, of those people that can be trusted to recognise their strengths and weaknesses, how many of those are scrupulous enough to act on recognition of their weaknesses? Again, this applies to the entire population.
In my experience this is what rules are there for - not to keep honest, intelligent people like you and me in check (well you seem honest and intelligent, whether I do is another matter, but I digress again), but to keep others from spoiling things.
This unfortunate behaviour of assumptions that most people show, is why I reject your argument that declaring extra time is analogous to declaring using a pen. It will be assumed that you used a pen in nearly 100% of cases, unless you state otherwise.
I can't agree with your twice used point that asking a dyslexic candidate to sit an exam without extra time is like asking a non dyslexic candidate not to use a pen. It's clearly extreme - the two are not really that comparable - but I do see where you are coming from. I have dyslexic friends that were only recently diagnosed, and therefore only recently got extra time in exams. However, before the extra time was given, they were still doing okay. Could I have done OK in any exams without a pen? Like I said though, I see the point you were making.
Regarding discrimination, choosing a dyslexic person over a non dyslexic person because of their "original thinking styles" does not strike me as discrimintion. It strikes me as selecting them for their original thinking styles which is surely a legitimate criterion, whether caused by dyslexia or otherwise. Throwing a CV in the bin solely due to the presence or absence of the word dyslexia - well that's obviously discrimination.
I can see the flaws in my suggestion (and you've pointed out a couple more) that extra time in exams be madatorily declared, but I put it out there because in my opinion it is better than the current system. I'm not so conceited that I think everybody should agree with me. The current system is a much huger problem (well I think it's a problem) of reliance on exams to determine ability. It irks me that some people are naturally intelligent and ace exams with very little work, and some people are fairly dopey and work their socks off to do well in exams. I think a distinction should be made between the two. I can't propose a way around this though.
It's possible that the reason I'm disposed against extra time in exams is becuase the only people I know that receive it are less intelligent than me, and I think our exam results should reflect this. I know that extra time does not magically boost your grades massively, but as it's getting easier to get a A these days, distinctions that should be made between candidates are disappearing. Perhaps if I had a friend who was very intelligent and dyslexic, it would be clearer to me how the condition hampers the expression of the intelligence. As it stands though, given all the time in the world, my dyslexic friends could not formulate a piece of writing that reads nicely. The limiting factor in these cases is intellect though, and not dyslexia. Maybe if I knew you it would help! This is all a bit off topic, and is really addressing the issue of whether or not exams should be harder. I think they should. Quite a bit harder. Then I think I would agree more with extra time, as there is a smaller chance that extra time will boost grades unfairly.
Ben