Aerodynamics / Aerodynamic Cost / Aero parts

No idea. I hope the gainz are massive having just bought a Zipp disc but I'm pretty sure, since the disc is covered so much by the bike, there's not going to be a great deal in it.

The chap in the Tyres thread talking about putting a cheap tub on an old disc had me thinking: Has there been many/any improvements in disc aerodynamics over the last decade?

I'm using a cheap old HED track disc, shod with an expensive tyre for this TT season.
Apart from slightly better aero, crr and stability from a wider track, what can be improved?

I can't comment too much on aero improvements because that's not my area of expertise. I was always under the impression that narrow was better because of the function of cross sectional area but, as the others have said, once you take into account a slight side wind you get a sail effect. You can make a better wing section with a slightly wider wheel - plus a wider wheel takes better advantage of the structural properties of carbon.

Structurally I think is where discs have come on quite a long way. I've got an old road HED too. Slightly lenticular. I'm not sure it is actually carbon - I think it might be glass fibres in a black resin and it's a kind of sandwich structure. Looks like a basic 0-90 degree weave. Bonded onto the alloy rim.

Modern wheels (like the Comete) look like they are typically made with pre-preg panels of unidirectional fibres running radially. It is much more efficient doing it this way: it is much stronger, stiffer and so can be made lighter. Those Lightweight discs are made a different way. They look like they are UD carbon tape 'spokes' bonded onto a foam core and skinned. The conical sides make the stiffest wheel for the least material, like a conventional spoke works. I think the new Ghibli wheels also have some kind of spoked structure inside to make it really stiff and a thin lenticular surface over the top. The HED really is an inefficient use of material in comparison and that is why it's so heavy.