Personally, I would love refunds to stay. If there are no real consequences (such as a potentially desastrous loss of income), why should we care to make the guests happy? It’s also a helpful indication that, even if all categories are green, not everything is well in paradise and we need to start paying attention. How else would we notice that?
It would be nice, though, to include more information regarding causes (we still have this mysterious catch-all category of “unhappy with visit”) of and remedies for unhappy guests within the game. I can imagine that many players don’t visit this or the Reddit forum (or not regularly enough) to get helpful tips from other players. Such issues that can drive a previously successful zoo into bankruptcy in a very short time should not hit players completely unprepared and cause them to give up playing, but should be fully explained in the in-game help. Maybe the first couple of Career scenarios, which are intended as tutorials, could be updated to provide better step-by-step training on guest happiness and refunds - maybe a scenario where one goal is to achieve zero refunds before bankrupting the zoo.