I'm running currently aD80 that has just recently passed 21,000 photos.
I bought it new when it was current, and since then I have only had the sensor cleaned once.
This wasn't a service, just a clean.
I'm now at the point where if I shoot at anything smaller than F11 dirt shows up on my frame. Shooting at something like F18 - F22 shows copious amounts of dirt.
Other than that it's performance over the last few years has been amazing.
I wish to continue this awesome performance. Should I send it in for a clean and service?