difficult one if they're machining only, as a lot of the stuff mentioned here will need welding even if only small amounts. If we're talking pieces that can be made from a single piece of billet then I'm sure they could do some nice stuff but would need to come up with some quite innovative ideas... and I'm afraid I don't have any lol

maybe Impreza specific tow hooks, nicely engineered gearnobs with the notch for the OE gaiters, engine bay caps etc as mentioned..

 

Coolant expansion tank spacers, proper steel wheel spacers to convert from 100mm to 114mm PCD.

 

+2 for harness bars