There is a mod for the hum. I haven't had a problem so I didn't do mine yet, but it's also one of the early J-wire versions (the one with the transformer mounted to the PCB).
My old keyboard was a frustrating mess too. The new one works great. You (or I) could probably sell the old keyboard and it would pay for the new one. The guys with membranes are the worst off of all, yet I don't see many people jumping for a new Fatar keybed. I'm very happy with mine. It took a while to sort out the wiring though, and you need to remember to order the cable with the keybed, else you are in for real fun.
I think all the Pro One's sound a note when you turn them on. All the one's I've seen do anyway. Maybe just the oldest ones? I dunno ... if the rest of the Pro One sound generation is good, you might be best to stick with that. If you get one with a dead OSC or something, then you're really in for it.