In the fly fishing world a 6 wt fly rod is what a lot of people get for trout. It might be a bit over kill for Crappie. I wouldn't think twice about bass fishing with a 6 wt rod. If you are buying one for Crappie I would think a 4 wt would be about the best choice. If you already have a 6 wt then by all means put fish in the boat!!
If you want a fly rod for jigging and can't find a spinning reel to fit the reel seat then why not use a fly reel? You can get them at BPS, WM, and other places for $20 or so. Just wind some fly line backing on your reel and tie about 20 - 30 feet of monofilament or fluorocarbon to the backing. I would think this would make a really good jig pole. It wouldn't cast very well but for jigs it would be a very sensitive set up with a lot of back bone.
Dan
Alright fish, I know I got something in this boat you'll eat.....Yep, the 'ol boat carpet seat cushion jig does it every time!