Done it on mine mate, makes it run better rather than a noticeable performance increase. I would'nt say dont do it, but if your looking for more horses, then I would look elsewhere first. If you looking to spend a fair bit of spondulux on it, then I would do your remap last!
i.e from experience, Manifold, high flow cat + Cat back system will free up lots of torque, defo 1st on the list! decent air feed, CAI, MSD'S + Iridium's etc etc, then remap the bugger!
Hate to plug, but Ive got a ported & Polished cylinder head going on classifieds here, looking at 10-15 BHP from that with a decent cam!
Hope this helps mate!
Otherwise..do as I have done.. all the above mods..cooper S Internals..running and 8psi Turbo kit
Cooper's can provail! Honest!