I believe Yahoo is worth the cash and DMOZ sucks. Might as well forget as most editors have their head up their azz. their are other worthwhile paid directories too like Business.com and Joe ant
I believe the quality of yahoo only really depends on your niche. If you are trying to target high value keywords, then yes a backlink from yahoo is useful, if you are going after more long tail keywords then maybe it is not necessary. Don't expect too much traffic from yahoo itself though.