I think the answer to the question is : It depends.

Since you bought your copy of 2005 from a discount store I'm guessing your a guy who wants to some programming from home and hopefully make a bit of cash while you're at it. In that scenario I think I'd find it hard to justify forking out on the latest version of visual studio - it's not cheap, after all. Sure, you get more features with it but .net 2.0 was a perfectly good language and you'll be able to work with it just fine.

On the other hand, if you're buying this for a company and you've got even a half decent budget then it's always a good idea to be able to use the latest technology. The increased productivity should more than offset the cost of buying the software.