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.