...now that electronics are so light and cheap, a TCAS or FLARM system could, at least, significantly reduce the risk.
Absolutely. Electronic conspicuity is the name of the game if we want to improve the accident statistics.
Yes, lookout is vital but no-one can see around their aircraft 100% of the time in all directions. I use TCAS at work but it doesn’t really fit with typical GA flight profiles.
I have FLARM, which will alert me to traffic that it perceives as a threat, getting more insistent as the time to collision reduces. It doesn’t tell me what to do but where I should look. If I can’t see whatever is causing the warning, I know I need to change height and/or heading to deconflict.
A properly installed and set up EC system should have much less in the way of blindspots than humans have when seated in light aircraft. It is a complement to lookout, not a replacement but in today’s crowded skies and in areas where traffic is funnelled under and/or between airspace restriction, I think it is indispensable.