I guess you don't agree with the old saying that happiness is belt-fed? I love full-auto for fun, but other than suppressive fire I would guess that the three round burst is probably more use in the real world. I don't like the three round burst capability because I was taught to use full-auto in short bursts like that by my own control.
But I agree with your comment about affordable. Even if the price of selective fire weapons comes down by repealing the 1986 law freezing the NFA registry, I don't see any way I could afford to feed these hungry monsters, no matter how much I like them.