My WM Antelope is about 15 years old and still in great shape. I have no ideas how many nights in it, but it got a lot of use.
A year or two ago I fluffed it out at home and noticed that it looked about as lofty as a 30* bag (Antelope is 0). I washed it, dried it thouroughly, and it didn't look any better. Short version of the story, after hearing my use:wash ratio, Western told me to wash it 2-3 more times. In other words, I opened it up fully and tossed it in the big front-loader w/a bath towel to help sink it. I ran one cycle, let it drain; I added a new batch of soap and ran a second cycle; and one more time. Into the extractor, then into the dryer on low heat w/a couple of tube socks w/2 racquet balls each. Dried for hours. The bag looks brand new.
You can overwash a bag and strip its natural oils, which are significant in maintaining the life of the bag. But in a situation like yours w/such significant use, you just need to wash it a few more times. Honestly, mine now looks more lofty then when new.