In my opinion, there's no reason to allow logging the same cache multiple times, with an exception of these grandfathered caches. It should be blocked by default and if there's a real reason to allow multiple logs, reviewers could have the right to do so. The cache count doesn't mean much and can't be used to compare cachers' experience, but allowing to log the same cache that is still the same is a bit weird.
Most people log twice by accident or because of multiple visits. If the cache has to be changed significantly, then it's not the same cache anymore and should be reviewed again (e.g. changing a T2 cache into T5). If one visits an already found cache again, the solution could be to have a "repeated visit" log type.
For events, I think one log per event is sufficient. Events are meant to be fun and not a cache-count hunt. It would be much nicer to simply write "I found 20 caches on this event" than writing 20 separate logs just to get the points.
I¨m not much into collecting points; longer caches that take me to interesting places are what makes Geocaching so great. Collecting points is OK but multiple logging just for getting points is an extreme. While GC is mostly about honour, it's not a reason to have flaws in the system.