"It seems to me, however, to be an awfully trivial reason to forgo all that fun - after all, you can't see the bonnet gap when you're driving, can you?"

Well such a strange thing to say, you can not see all the muck on you wires when you drive but you still like then to look clean.
The Caterhams have much more powerfull engines but they do not have such a big gap any yes i have had one and an Atom all fun cars.
When I pay quality money I want quality. I went to Tatton Park car show a few years ago and there was one of those awfull kit car Morgan copies with an ally bonnet, not a nice car at all but it only had 1/4 inch even bonnet to wing gap, it wad an insult