My understanding is that an analog joystick works OK for paddle games since they are based on a potentiometer and can be mimiced by the analog setting on the U360. This works for the 270 degree drivers. Not a true arcade feel, of course, but playable until I can get around to builiding a dedicated driving cabinet.
For the spinner (and 360 degree) games, I'd tend to agree, because using the increment/decrement functions doesn't seem to allow control over the acceleration of the "spin". However, it does seem to work well enough to play a number of games (e.g. pole position, supersprint) on it.
I don't know how the MAME controller code works, but it seems like there's two ways this could be enhanced
(1) A variable increment/decrement value based on the analog joystick level. (Maybe this is already done.)
(2) A setting for the U360 that gives relative output (i.e. the increment/decrement is done by the U360). This is similar to the Mouse Pointer function that already exists. I tried Andy's Mouse function, but it seems to make the U360 operate as an actual "mouse" with only 3 buttons.