I wakeboard, (Davids son Harry)
We used to ski and board off a valiant 490 with a 60hp yamaha and it did the job fine. Not much of a wake...but it was ok other than that.
If you want to really progress in wakeboarding, to the point where your getting hige air and pulling flips and grabs and the like then yes you need some sort of tower, if you only wakeboard casually (like us) then towing from the transom is fine.
The bigest problem with the low transom on the valiant was the rope dragging in the water, buy the thinest rope you can if its likely to drag in the water and it wont make much difference.
We have about 500mb's of wakeboard video from our last Lake District holiday behind the new boat which ill host some of when i get around to it.