That's what I thought until my wife bought a vehicle with both.
The ventilated seats are nice, but as long as the AC works well I don't think the vented seats make a big difference. When switching from her car to my car in the summer, I don't really miss them. My wife's new car is also our first one with a heated steering wheel, and I'm hooked.
The first vehicle we owned with heated seats was a 2000 Jetta GLX, and that spoiled us. Even when I bought a Focus ST, I had to have them. The Focus' heated seats are awesome because you start to feel warmth in just 1-2 minutes and they are nicely warm in ~5 minutes. In really cold weather (<10F) they start to warm you much faster than the cabin air heater.
But given recent experience, I would give up heated seats and ventilated seats before I would give up a heated steering wheel. I'd much rather have warm hands and a cold bum than vice versa.