See and avoid is not something that can't be taught.
A new Mode C txpdr can be bought for under £1000. I don't nescessarily agree with forcing people to fit Mode S if they have a servicable Mode C transponder but I am of the view that the majority of aircraft should have a transponder. If not we'll be regulated in other ways (airspace for example).
Look at the USA, many "homebuilt" aeroplanes have them. It seems that they are not too hard to fit in the USA are they? Why is that? Different mentality perhaps? Of course in the USA you can fly your homebuilt or ex-warbird IFR with the right kit. You'll find many second world war warbirds with a GNS430onboard. There are many Mode C Vales, where aircraft are not allowed without a Mode C txpdr unless previous agreement with ATC has been sought. Sounds fair enough to me.....