Couldn't agree more - consider how many Mini's are out there and how many people are into heavily modifying them and you'll realise you've alienated most of your potential buyers.
If it's in great condition, one owner, low mileage, good spec and full BMW history there is no reason for it not to sell reasonably quickly.
Most people will instantly assume (with mods) it's been driven hard (no matter how much love you've given it) and see that adding up to £'s in repair bills down the line - remember Mini's are pretty much the most expensive 2nd hand small cars to begin with.
There's also the question of insuring it.
Put it all back to standard and sell the bits separately, I'm sure it will be easier and possibly get you the price you're looking for.
Cheers, Geoff.