I am not getting your arguments, or maybe you are not getting what the community is building with their resources.
There are many playerunitevents that are not order events that are used, and used by multiple libraries like item systems, death detection, not to mention the infamous UNIT_ATTACKED that is still useful for detecting the moment the animation finishes. Hero leveling is also commonly seen lately.
Saving a few dozen handles is the smallest benefit to be gained, however in many maps I've seen there is room for saving hundreds.
In either case saving RAM is worth it - and I mean just for the sake of saving RAM this is worth it. Fewer handles is the lower concern although it does help if you are using something like handle ID offsetting (keeping handles as low as possible), in such a way this contributes little (but it does contribute).