as a mid 20's guy i think hammond is a huge part of why the show rocks. the way him and clarkson review cars is the best i've ever seen. why? easy, you can see the passion flying out of them. its why american automobile review shows dont work, they approach it with technical precision and sterile gloved instead of the proper way; like a kid at recess.
the ONLY top gear ilike is with clarkson, hamster, and may. they work. hammond has the young hothead perspective, may is the kind of proper "this is comfy so i like it" guy that pompous business men can relate to and clarkson... well... clarkson is like an irritable one eyed bulldog that balances his abundant flaws with a child like lovable nature that makes us want to see him driving cars that take 40 years off his life (is he like 70 now?).
ya can't ditch any of em but the one i relate least to is james may. hell, though, you can't have "the two stooges" it just doesn't ring like the original...
hammond. he really doesn't add much to the show besides appreciating american muscle cars. he doesn't have much of a personality either.
jeremy is great for his brash personality and propensity to conjure up some controversy. may is fantastic for being the voice of reason to jeremy's maniacal behavior. may also brings a bit of sophistication to the show.
I'd keep all three, but get rid of people claim that everything is staged. Or indeed anyone stupid enough to miss the fact that Top Gear works because of all three presenters and that by removing one, the whole thing would lose it's appeal.