I was glider only for almost 20 years when I finished my power ticket
a couple years ago. I still struggle with maintaining a fixed
altitude!

Gliders are WAY more fun if you are flying cross-country but power is
pretty dang handy for transportation. I wouldn't sell the glider. You
will miss it like you can't imagine. You can get into power for
cheap. My plane with fresh overhaul came in around $10k but I put a
LOT of work into it. See http://www.antiqueairfield.com/ for a recent
trip write up.

Glider flying makes transition to tailwheel a LOT easier and
quicker.

Glider hours don't help much costwise till you go for the commercial
power. Than it can make a significant difference, especially if you
have cross-country hours.

There have been several good books on transition to gliders but none
on transition to power as far as I know. I've considered writing
one. Example: I was well along in planning a relief system
installation in my airplane when one of my buddies pointed out that I
could simply land to take a leak. I wasn't impressed until he pointed
out that I could also take off again. That was a revelation!

Matt Michael