"I'm wondering how often you folks have your skis tuned/sharpened."
Depends who's doing the tuning. Most shops just run them through the machine. Do that often enough, and you won't have much left after a couple of seasons. On the other hand, a careful de-burring, touch up, and wax can keep them the skiing machine they're supposed to be, and discover preventative maintenance opportunities that could save you grief later. There's another thread somewhere on tuning where neglect is deemed harmless, though I've had bad edges let me down. Like Scalce, I enjoy the process, the touching, the familiarity with my vehicle.
"I'm doing a little analysis about the wisdom of buying skis vs. paying for demos."
The problem isn't the $ cost, but the time in the various queues for the process. I'd rather spend it skiing. Although skis do make a difference, at a certain point you'll make more progress "running what you brung," that is, learning the characteristics of your skiis, maximizing their strengths and avoiding their weaknesses. Find a a ski you like, buy it, then rent when conditions require it. Getting to know your bindings is important, too.
"Now, considering the initial $600-$1200 outlay for skis/bindings and depending on how often I might have my gear tuned, it just may be more economical to rent demos then to buy new gear and keep it tuned."
How often do you ski? Do the math. Many recreational skiers would be money ahead if they just rented for their few day trips and one vacation. Me, I have 7 pairs--4 race, 3 for fun--but its my sport, and I live 30 mins. from the mtn..
"How often do you tune--every time you ski, every other time, every 5th time?"
As conditions warrant and my time permits. Nothing beats a fresh coat of the right wax.