I'm not sure what situation gears aren't appropriate for, but you know it more than I do. While I don't use most of my 18 gears regularly ( there seems to be a small handful I mostly stick to ), I love being able to shift to a lower gearing when I'm climbing, or fighting a headwind, and a higher gearing when I'm spinning out at 20 mph. It's a little hard for me to picture giving that all up. But I'm doing 500 miles per month, and haven't needed any maintenance to the derailleur.

Anyway, I wonder if you could rent a couple of bikes on a couple different days, that are already set up with 3 and 10+ gears, and have some fun at the park, before deciding what to spend your money on?