It's such a shame, I thought he'd be the next big thing after he won the Nissan world series, race of champions and led a lot of his one and only GP2 season. And after a rough start at Renault, ended up putting the experienced Fisichella in the shade by the end of the season with some good performances. He's also a Finn! But unfortunately for him, Hamilton is just faster.
It should be said my talent spotting is pretty rubbish though. I remember thinking Massa would never achieve anything in his debut season at Sauber, and thought he didn't deserve the Ferrari seat and then he proves to be a title challenger last season. My next tip... Hulkenberg!
I agree Heikki would be a very good midfield driver, seems to keep his head down and put the effort in, and to be honest most drivers wouldn't compare well to Hamilton.
Oh and to answer the question... if you have to give the new parts to only one driver it has to be the fastest or the guy with the most points.