Another drawback is the very significant loss of rudder feeling at the helm because of the double mechanism.
I cannot speak for the twin-wheel set-up on the Comet 41, but I've sailed boats with all three configurations - tiller, single wheel and double wheel - and I don't think there is any siginificant difference in feel between the single and double wheel, if they are set-up and tensioned properly. Obviously, the tiller gives the best feel, particularly upwind, but the conveniences of the double wheel are well worth the slight loss of touch.
In addition to allowing easier access to the stern, it also allows easier movement of headsails from below, during sail changes (more important for racing but handy for cruising, as well, if you're not using furling), and, in my opinion, it is a real pleasure for extended downwind driving. Since everything is done in carbon these days, I don't even think there's that much weight difference between 1 wheel or 2 (OK, maybe a little, but I'm thinking the builders have got this optimized by now).
On the other hand, for solo sailing I would opt for either a single or twin tiller (depending on boat length) because most of the time the autohelm is driving the boat and having no wheels in the cockpit creates a lot of open space, which I like. And for those times you feel like steering, then you have the nice touch of the tiller while leaning back comfortably against the lifelines.
Both Comets are gorgeous boats, but I'm in agreement with Eric that the dolphin nose on the new one is a bit inelegant. If I was racing I'd want a carbon sprit optimized for IRC. For cruising, something simple and preferably detachable or retractable. Also not a fan of teak decks, even though they look posh. Do like all the opening ports for circulation. If someone offered me either boat, I would take it happily.