KLR650 clutches seem rather robust, from experience of others. Assuming the clutch hasn't been abused (as in, slipped excessively), I'd expect service life beyond 25,000 miles.
Regarding adjustment, the clutch cable is adjustable at BOTH ends, at handlebar lever and also at actuator lever. Have you exhausted adjustment at both these points?
Service manuals have service limits: 2.60 mm/0.102 in. friction plate thickness; 36.4 mm/1.43 in. spring length ('96-'07); steel plate warp 0.3 mm/0.012 in.
Don't know of any tricks for clutch life-extension; with components complying with these service limits, should be adjustable to serviceable condition, IMHO. Not terribly hard to check out (can be disassembled without removing crankshaft nut); not terribly expensive to replace parts.