I have recently done some cheap and cheerful mods to my mini. It now performs so tight and solid! I would recommend poly bushes all day long even if you want to keep the car original they are a fantastically sensible upgrade to better the minis handling, without spending much money. The earth strap was another purchase which was in need of a replacement. I think the electronics have perked up because of this, who knows, maybe its just playing games. I also spent a lot of time sanding the old black paint off the seam strips to change to body colour. The colour I chose is the exact paint code (NMN) which the car came out of the production line with. Its not an exact match but I like how it harks back to the cars proper spec.
I hope this update helps because it really has improved the driving feel, ultimately it made me feel like the car has doubled in price, its that good.