This question is asked all the time here and most of the time, I just bite my tongue and go on.  Yes, maybe in ideal situations you "might" be able to do an acceptable job drilling with WAAS.  But I don't think there is anyway you will get an acceptable job from WAAS planting row crops.  In less that ideal situations, it is not uncommon to see 3' jumps from WAAS and time drift is definitely there.  I have spent several years using various WAAS systems to "find the row" and find the marker at night and in no-till.  I have seen how close WAAS can be.  There is no way I would even consider a WAAS steering system for row crop work.  I am not saying that WAAS steering systems don't have their place, they do.  But planting (esp. row crops) is not one of them.

Every body seems to be looking for the "cheapest" system they can find.  They are oblivious to whether the system will do the job they need to do.  It would seem to make much more sense to start out with a system that will do the job and that can upgrade to higher accuracy as the need arises without having to junk the complete system.