Vintage will not automatically mean good sounding at the least. Build quality will be very inconsistent and most of them would most likely have disappeared already for one reason or another. The small number of vintage instruments remaining makes it more difficult to actually find a good one, more so for great sounding ones. More than just the Super Strats from the late 70s, this also applies to even the coveted and highly-priced 54s, 57s, 59s and 63s.
Modern built guitars, on the other hand, have a higher chance of having more good sounding guitars in one production batch. This is due to current technology that allows for a very consistent build from guitar 1 to guitar 1,000 and from parts to parts. So assuming that a bunch of guitars with parts and modern build quality being equal and of high-quality, there are more good sounding guitars now than vintage ones.
The hunt now is not for a good sounding one but for that exceptionally great sounding one.