The thing I don't like with more than 8 speed is not just the cost. It's the robustness and error margin of the whole shifting system. 8 speed and less give wide enough spacing that both friction shifting is easy and indexed shifting is flawless even with old/dirty cables, not perfect derailleurs etc. I recently swapped 105 10 speed setup for an 8 speed Claris/Sora one - shifting has improved. Same bike, same mechanic (me), same housing and cables.
Got the alu frame at a very low price, and it's tube is too thick for mounting DT shifters - the ones available at least.
MTB has friction shifters, 3x6, and has been going strong since 1996. No need for a change.
I cycle a lot. Don't have a car - it's my main means of transport, my sport, passion, hobby. I fix bikes for hobby, for friends and for money sometimes. My conclusion is that for the way my friends and I ride bicycles, most new stuff is just made to make you spend more money. It lasts less, costs more, is more difficult to repair, maintain. And it brings nothing really better - not to the way we use bikes. Climbing mountains, riding to work, hauling groceries etc. I even ride with some amateur racers occasionally. When I'm dropped, it's never the bike.