An 88' KDX is a nice bike, nothing wrong with air-cooled. I owned an 83' back in the day and knew of a few others in that timeframe. All good bikes. I'd just be a bit nervous about parts availability - almost 19 years old now... Perhaps someone else here can chime in on that. Maybe try posting in the KDX forum if you haven't already.
XR's are great, bulletproof bikes. Though the power is much milder than the KDX.
From the sounds of it, I'd say save up some $, sell your bike, and buy a newer KDX200. Or try a 250 2stroke MX bike if you want "fun and powerful"!
Best of luck...