I've recently had an mx5 remap which went from 158hp to 180hp and although the numbers aren't huge it has really woken up the engine.
It's not just about top end power, torque is up across the range, all gears are unlocked to 100% throttle, fuelling has been tweaked to use less fuel at idle but provide more when it's needed, flat foot shifting, rev matching, 4 switchable maps (tuned map, race rom, standard unleaded and valet) and the engine runs beautifully with not so much as a pop or bang.
£574 well spent.