I played some 4-player Mu and found myself not bidding at all for several hands. This may not seem remarkable unless you've ever played Mu or most any other game with me. I haven't played all that much 4-player Mu, so this may be more normal. See, I had fairly flat distribution. Things like 4-4-3-3-1 and 4-4-3-2-2. The first time I was the dealer and decided to not bid and see what came up. Neither of my 4-card suits came up, so I just decided to stay out of the bidding entirely. The chief ended up not making the contract. The second time, I was the last to bid, and none of the other 3 people had bid any of my 4-card suits, so I again decided to stay out of the bidding. The chief went down again. And, having not put out any cards, I was not chosen as partner either hand, and i believe I was leading at that point.
Most of the contracts in the game failed, which is why I think I was later able to get a 1-bid with no vice. I had 6 yellow cards and was able to have complete control of trump. Sure, I only got a 10-point bonus, but I raked in 36 triangles, giving me a 20-40 point net gain over everyone else. It might have been tempting to bid myself up in order to get a larger bonus, but then someone would likely have put at least one card down, and I don't think my net gain would have been as high.
I think I still prefer 5-player Mu, but 4-player Mu is fun as well.