Well, unless you are going for a straight downwinder and have someone to pick you up, upwindability is relatively important. Maybe not as important as drift and stability, but still. Upwind, it could be argued, is on the top of every style of kiting except one that is dedicated to only going downwind. Any trick you do that takes you off your tack (jumps, surface tricks, ripping in the surf) will be pulling you downwind, so the faster you can get back to start is the faster you can get back to what moves you.
Kiting is decidedly less fun when you are fighting upwind and can't seem to get there fast enough.
I don't think a kite that upwinds well is going to drift very well or turn as well. It just means that when you're on the outside working your way back up you need to be as efficient as possible and remember that every time you send it off the perfect ramp it's one less wave that you'll be getting.
My priorities are that the kite delivers smooth power through the turns which match my movement heel to toe, turns fast enough for me to be able to keep the kite low after multiple turns, and being able to dump power not just while riding a wave but to make the inside turn while getting the edge planted fast and heading back out. Depower to where the bar is at arms length and the LE is flapping as it goes fast across the window without yarding you.
Another nice feature that some of my kites have had is coming back up after you dip a wingtip - I don't have to relaunch very often but it's nice to be able to smack the water and come out of it without problems.