Only third-party sellers will sell the Sony PRS-T2 on Amazon, and your Amazon gift voucher balance can only be used on products stocked by Amazon themselves, not for items from third-party sellers.
It's been said the T2 will be released this coming week, but the Sony site still just states pre-order and doesn't give a specific date.
Look on
ebay for the price you are likely to get for a new Kindle Touch, expect to make a small loss of maybe £10-20 though, and you are never guaranteed anything selling it on ebay (unless you set a reserve price).
Although the Amazon press conference is due next week, it may well be October or November before they start selling a new Kindle, and it may well be available in the UK at the same time (AFAIK it's only been the Kindle Touch that was delayed in the UK, the Kindle 3 and Kindle NT were both available around the same time in both the US and UK). Either way, it's probably worth waiting to hear exactly what is announced at the press conference in a few days time before making up your mind.
On a final note, all e-readers are to a certain extent quite fragile. It's the screen that often breaks causing people to complain about the lifespan, and both the PRS-T1/T2, and Kindle Touch are about as fragile as each other. Whichever one you buy, choose a case for it if you take it out with you, and don't carry it in a bag along with anything hard that may break the screen.