It just depends. There are some cases where valve seals can make a DRAMATIC difference. Probably the best example of this is the early 103 engines with defective seals from the factory. Replacing them with the updated ones corrected the oil usage problem entirely. With other engines you just never know.

You should start by determining that you don't have a cylinder related problem. Do this by doing a compression check or better yet, a cylinder leakdown test. If the rings are holding compression good, then give the seals a try.

Good luck,