From a technology standpoint, it's all framework version 2 and it's very little effort to achieve. The differences in 2.0, 3.0 and 3.5 are just additional library code and some compiler syntactic sugar.
It's not like you need to change anything over; by targeting framework 3.5 you have more options.
From your teams point of view: Yes it's worth it. Nobody wants to work on old code-bases. While you're in the heat of development, you might as well utilize the most current stable technology.
