[swarmee]

It really depends. There are plenty of cards that would benefit from grading just to confirm authenticity.
When I'm looking for cards to grade, I put them in a couple of different piles.
1) Part of sets I'm working on in a reasonable condition (as in, I'm not going to find a better one for cheap within a year or two).
2) Cards that would go up in value about $20 (3x grading fee) compared to raw.
3) Cards that are rare, bizarre, or reprinted enough that the average collector would rather have a graded card because that means it's been authenticated.

I still have some "gem mint" (to me) 1981 Topps Basketball cards that I haven't sent in, because unless they get 10s, they won't have been worth grading. Since I'm not working on the set, I've never sent them in.