The problem is that lookout has a limited effectiveness.
I've often flown under an RIS, with 3 passengers, and we were all looking out for traffic reported to us. Most of it we never saw.
Also, at best, the angle of view from a cockpit is limited. You could be going at 100kt and another plane descending at 180kt could fly into you from say your 4 o'clock.
People don't like to be told that the "old Mk1 eyeball" (to quote the traditionalists) is actually pretty useless....
In reality, mid-airs are extremely rare. If they were common, something would have to be done about it. Just as well, since most people really do believe that keeping a lookout avoids hitting something. Those that you spot (and perhaps try to avoid) would nearly always not have been on a true collision course anyway.
The only potentially effective way is mandatory Mode C transponders, and TCAD/TCAS which starts at about £15k. Even then, you won't spot most of the reported traffic but at least you can take your own avoiding action.
I agree the circuit is the most dangerous place. Which is why I don't like overhead joins. One is asking several pilots at once to all head for the same area, all at 2000ft AGL. Usually, one cannot spot all of those who are known (from the radio) to be arriving at the same time. In those conditions, I've aborted the join and came back later. But there isn't a solution to this, if several planes really do arrive at the same time. Not under VFR. Under IFR you just put them into holding patterns so in effect they are doing overhead joins but at different levels
