I know how you feel - I learnt how to drive in an R56 One, and the throttle delay IMO is totally un-acceptable. I lost count of how many times that I got bogged down in the middle of roundabouts in 2nd gear, so frustrating. Some would say stick it into 1st gear, but, your still doing about 15-25 mph, and at those revs, all the car would do is jump and jolt, and it would be revving like mad. Not to mention what the gearbox would be like
If I were in the market for a Mini One, I would defo try get one with the sport button - However, I don't think the Sport button can be retro-fitted, because it covers more than just the throttle response.
"The new EPAS (Electric Power-Assisted Steering) makes a significant contribution
to the pin-point behaviour of the new MINI. Speed-related power
assistance guarantees low steering forces when parking and, at the same time,
precise responses at high speeds on the motorway.
The electric system offers the driver a choice of two different steering control
maps. The standard set-up ensures a well-balanced steering response in all
speed ranges. The second map is activated when the Sport button is pressed
and the power steering becomes even more direct. The electronic map for the
accelerator is also modified by the Sport button to give a more instant response"
If it was able to be retro-fitted, then I think it would very very expensive. There must be some other sort of throttle sharpening method out there!!!