i have had mine in for 17500km (put in at 5000km) and other than the odd limp mode when at zero throttle position there has been no other problem..
i would suggest you try for a manifold cleanout from mitsu (tips on getting this done in the various threads about surging and limp modes and fuel usage etc). I only suggest as you have already got 50K's of buildup in there...
Theres some evidence that ChipIT can eliminate the limp modes and GLXRAlex pioneered disconnecting the throttlebody to achieve the same result... (both require some $$ investment in either a chip or scanguage respectively)
Personally my limp modes are so infrequent and i cant really justify buying that kind of equipment for a bizo vehicle (although that stance is somewhat slipping and i will be on the chip bandwagon soon enough i think
I am not sure as to the effectiveness of the wynns stuff? my guess would be that getting mitsu to do it properly would be advisable!
DO IT!! best (and cheapest) mod so far IMO