I'm in your area. I'm down, though I think that Whiteshark has some points and we should maybe refine the rules a bit.
I'm a musician. I generally don't risk my hands with breaking.
I use SuperSafe type helmets in my Karate class, so occasionally we do wind up uppercut palm striking to the dome if someone ducks their head down/leans their face forward. I'd imagine that shot, to the nose/face or chin would be a good one. I could also see someone with frail hands/wrists and/or little training using them instead of knuckles, even to the body; aside from that, I don't think I'd use one.
A lot of the good Pancrase shots were less the palm heel strikes that take the place of straight 1-2s, but slaps with the the heel, replacing the hook.
P.S. If you do this test/challenge, you're going to have to spend a little time practicing with palm strikes on focus mitts, because the angles you need to throw your straight punch replacement palm strike are slightly different than a punch which makes contact with the knuckles. You're bound to feel more awkward doing something you're totally not used to and messing around with on the fly in sparring, which makes for skewed test results.
I'll be interested to see the results of this. On a prima facie basis, punches have both more reach and more chance of reaching their target due to being a smaller object than an open palm.
You could have a round where the combatants can throw punches with their jab hand and only open hand strikes with their strong hand. That might actually be interesting.