Would it be more appropriate for the VA or anyone else to say "Thank You For Your Soul", instead of "Service"?

Yea, that's not creepy at all.

I am uncomfortable with the thanks for your service line. It is, however, preferable to thanks for your soul. The second sounds like I just made a deal with the devil

Ha! No...frankly, the whole, "TYFYS" thing weirds me out enough as it is. I mean, just the other day, I was talking with someone at the range, and brought up an experience from my time in the Military as an example... the guy suddenly goes all "respectful", and says, "Hey, man... thanks for your service", and I'm just like, "Ummm-yeah...thanks...but I thought we were discussing whether or not the Barksa is a crap red-dot compared to an Aimpoint".