IO540,
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 think this would create more problems. I agree that technology solves IFR problems, but remain suspicious that for plain old vannilla VFR, technology seems to add complexity and procedures for dubious returns. As has been said, most mid airs are in the circuit and any half decent TCAS system would be going absolutely banannas as it approaches the ATZ! Yes you can switch it off, but that is another line to the checklist, something else to miss and something to distract. TCAS is a good idea for an airliner where seperation is ATC maintained 99.73% of the time and any Resolution Advisory is a rare eye-widening event. For the VFR bimbler in the open FIR you can fly pretty close once viz is established without feeling in danger and Resolution Advisories would be common place and needless in most cases. I'll wager that it would become next to friggin useless once you have tired of the number of alerts vs the number to real potential VFR conflicts.