I can either afford an A4 2.0T or an A3 3.2 sline.

 

get the outgoing 2.0 model and with the money you saved mod it

 

That is a very tough call. I don't think the money saved would be worth it, if you consider how much better the new platform is going to be. It's going to handle a lot better... likely be stiffer and quieter... If I was spending 'new car' money, I'd spend a few more grand and wait for the 08.
However, if the B8 looks as fugly as it does in some of the pictures I've seen... I'd be torn!

The 3.2 with DSG is absolutely amazing, though... So much fun!