I went to Reading every year between 2006 - 2010 (and went on a day ticket this year...), and I bought my tickets in the early bird sales for the first few years as I knew I wanted to go regardless of what the line up was. It depends - if they say it's a load of bands you dislike, will you still want to go?
I would always advise that if you have the cash now, buy them at the £210 - that's 2011's price and it will doubtless go up when they go on sale again next year (I know they've extended the pre-sale; back when I went it was only a few days at the end of August, but it looks like they're letting you do it all 2011 from what I can see).
Where did you find them for £150 in August!? Honestly, they escalate in price the closer you get to the festival so I would have serious alarm bells ringing if you found them cheaper than face value. This list is of the only authorised agents for Reading/Leeds tickets http://media.livenation.co.uk/fido/p...0Agents(1).pdf
and I would seriously not advise you to buy from anywhere else!!
So in short, if you're all certain you're going to go and you don't care what the line up is, buy them now
. If you would rather pay a little more and buy once you know the lineup then get them then (but they will be slightly more expensive and it will be much more frantic trying to get tickets, you will need to be online the second they are released as fans of the bands who get announced will start buying them up ASAP after the announcement). And whatever you do, don't buy from an unauthorised vendor!!
Have a wonderful festival and pray for sunshine!