As I mentioned before, my view is that the radome black was dropped because it wasn't particularly effective (in terms of improving the radar picture) and therefore unnecessary. I've never heard of any other reason why it disappeared so I can only assume it simply dropped out of fashion!
As for 617's Vulcans, I have no idea why they opted for black-less radomes either. The grey/green finish with white undersides and a non-black radome wasn't unique to 617 but it appears to have been applied to all of their aircraft for a period (or at least all the ones wearing their markings) and I seem to recall there were one or two other units which had similarly-painted examples, but 617 seemed to be the main recipient. All very odd!
Camouflage; well yes, most of the early camouflage schemes were applied in gloss but the wrap-around grey/green was definitely applied in matt finish. I suspect most of the later Medium Sea Grey/Green/Light Aircraft Grey finishes were also applied in matt too as they contrasted starkly with the gloss-finished B2(MRR) aircraft - doubtless there were exceptions though! I would assume that gloss finishes were abandoned when they switched from grey/green tops with white undersides (and started applying Light Aircraft Grey) the only exceptions being the MRR machines.