The only advantage I can see with allowing voting is that it might cut down on people bumping a trac report with "I want this too", which is worse than someone voting. Given that we haven't really had a problem with that, I don't see the need for the voting.
The sort of things that don't get developer support early on (whether that support consists of "sure, I'll do it" or is more "patch welcome, here's some suggestions") are generally not going to be implemented at all by the core team, and may not even be accepted, though these are usually flagged as such.
I think a useful addition might be some (completely optional, and only developers may fill them) fields to specify things like:
1. Acceptable with a patch (this allows filtering of suggestions for new devs with stuff that isn't being actively worked on.)
2. Perhaps some indication of difficulty level of the above?
I know I'd be willing to go through some of the FR's and fill in some of the above fields if I felt that it'd be useful for new developers.
That's really what trac is all about, after all
Cheers,
Jonathan