If you keep it in good shape, I don't think there would necessarily be a huge drop in value between ten and fifteen years of age. At both those ages, the condition matters at least as much as the actual age. For sure, in absolute dollars, a brand new RV is going to lose a whole lot more value five years on than a ten year old one--and I suspect the same is true even as a percentage of what you pay.
As far as maintenance and repairs go, the house part of most any RV does require ongoing maintenance and the occasional repair. Appliances can wear out, of course, but the majority of work is more along the lines of handyman jobs and resealing stuff. The van chassis on most class C's tend to be pretty reliable and trouble-free, aside from the usual expected wear items like brakes and hoses and belts and so forth. My class C is over twenty years old now, and over the six or so years I've owned it the main repairs I've had to make to the chassis have been brake work (sticky calipers needed replacement), ball joints (the seals wore out, letting the permanent lubrication escape), and shock absorber replacement. All of them I'd categorize as wear items, though admittedly not especially inexpensive ones.
