I've got a 14'x14' Snowtrekker with 4' sides. Like most things, it's a matter of perspective. It's much more roomy and comfortable than my 11x11 with 36" sides but doesn't have the standing room of the 5' wall tents. In my case though, the shorter sides means lower weight so better to pack on animals.
If just for truck camping where weight isn't an issue, and it's the same setup time, I'd hold out for a 5' sidewall to make it comfortable. Otherwise, for a base camp truck setup I think I'd always second guess myself and wonder if I should have gotten a 5' sidewall tent.
IF it's an incredibly good deal that you can afford now, and be able to resell later when can afford a 5' sidewall tent, then 4' certainly could be an option in the meantime.