If it's been well cared for, I wouldnt worry about the mileage too much. If the engine has had regular oil changes and valve adjustments, it should be good for a long time yet. Other than those mentioned I'd check:
Suspension - likely past its prime...ok, you can prolly deal with that. Just make sure you've got some damping in the shock. If it's toast, there are many original C-10 shocks around as alotta folks replace'em.
Bearings - the C-10's F wheel bearings are too small for their load. They often require replacement around 25-30K miles. This bike should be on it's 3rd set. They arent expensive, and are pretty easy to replace. Dont wait for them to fail completely - they'll strand you somewhere garanteed.
Steering head bearings - check'em. They really arent so much affected by mileage as time. 24yrs of service & weather, with no lube, they're prolly done. Replacement isn't hard, just takes alotta time
Cam Chain. C-10's have an automatic cam chain adjustor which sometimes doesnt. Chain makes a hell of a racket at idle if it's loose.
Waterpump - prone to leak/fail on high mileage bikes
If the bike is in as nice a shape as the pic would indicate, I think it's a great deal.
My plan iwth my own C-10 is to run it another 50K miles to 100, then sell it cheap to a soldier or student who can use it.