Dick, a controller can be busy from things other than sheer numbers of aircraft on frequency. There is a lot we do in the background that you wont hear it on frequency There have been times where I have only had a handful of aircraft yet being working like a one armed bandit. All it takes is a few unusual things and you end up very busy very quickly.
Most low airspace controllers will monitor the descent profiles of aircraft when they have the spare capacity. For example, there have been several times where I have questioned an aircraft that was 0.5NM off track after the initial fix on an RNAV. More often than not they are just doing a visual approach, but if I see it I will ask.
Ultimately I genuinely believe there is some room for improvement in the system, especially now we have ADSB. We don't really want to be the people that waited for an accident to happen before we changed things, even if the chance may be small. If we have the technology, use it to its capability. My ultimate question is what do we really have to lose by giving some of dicks suggestions a go? Every time I plug in at an ATC console I try and do a little bit better every time, perhaps the overall system could do with the same approach.