The A2 is too light and the power is going to the wrong wheels for anything over 150bhp to count.
When accelerating, all the weight is transferred to the back, the front end goes light and the wheels just spin, especially in the wet.
At the outset, the emphasis for the A2 was economy and practicality, not speed and fun, but when they realised it wasn't attracting market interest, Audi realised something must be done, so the Sport model was introduced and the 110PS 1.6FSi engine came in in 2002, followed by an uprated diesel in late 2003.
I firmly believe that an S model was also in the pipeline, but the decision to stop the entire A2 production was taken in mid 2004, so it never appeared. What would have been done to spice up the standard A2 is anyones guess, but a 1.8T is probably the favourite choice, almost certainly the same 150PS unit as fitted to the front wheel drive TT. How the problem of putting down the power would have been overcome is again unknown, but my guess is harder rear suspension and re-designed ESP systems.
I've taken the 1.4 TDi 90 to just about the extent of its capabilities now, just about 140PS and near enough 250 lbs/ft torque, which is 1/3 more than the box is rated at! Any more than this and I suspect the bottom end would fail and I'd have bits of con rod sticking out of the crank case!
Cheers,
Mike