Tim
I've no idea. Presumably your point is that American golfing visitors put more into the local economy than locals or students ? If you were using the amount of revenue of the Links Trust attributable to US golfers relative to students and locals as the yardstick then perhaps that might be the case (I've no idea, haven't seen the figures). I'd imagine it would certainly be the case if you looked at spend per capita. But that's not taking into account visiting golfers from elsewhere.
However as significant as golf tourism is, and US golfers are only a part of that remember, it's not the be all and end all of the St Andrews economy. If the next US President were to inexplicably ban US citizens from visiting the UK, that would certainly have an impact on St Andrews. Particularly certain sectors such as high end hotels, but shops, pubs and other businesses would continue trading. For instance the town would be full of (high spending) students as usual.
My point being, St Andrews doesn't depend on visiting US golfers.
Niall