Many pancake compressors are oilless in design (and also tend to be very loud), so the moisture would be the only real issue. I use an oilless compressor now, but I found one that is nice and quiet, which I am very happy for after the previous air compressors that I've used.
I dislike cleaning kegs too, though like you all said, it is still better than bottles!
When I get lazy, I've built up over 20 kegs needing a cleaning as well. Sometimes I clean during a brew day, other times I find time at night to do a few here and there. I rarely remove the posts unless there is a leak or a problem.
I did build a keg washer, but I don't really use it that much. I find that for kegs that have build up, I really need to get in there with a brush, and then at that point, it is just easier for me to spray it out with the hose, rather than put it on the keg washer. When I was using the big 55 gallon HDPE barrel though, the keg washer definitely came in handy. If I were to use sanke kegs for anything, the keg washer would definitely be helpful for that as well.