I agree 90% ...
I bought some L'oreal foundation a while back and was disappointed- it was watery and just looked 'flat'. I'm happy to spend £30 on this because it lasts me 6 months.
On the other hand, my DD aged 25 struggling with student debts etc buys cheap make up on the whole, and she looks gorgeous.
You've got to remember that high price tags cover the counter assistants salary, ( your 'free' makeovers) , the advertising , the packaging, free samples etc etc. The basic ingredients of many high end products are probably the same as cheaper stuff.
Bobbi Brown lipsticks ruined my lips- they sting after using the lippy and dry/ flake like nothing else- same happens with Rimmel but at £5 a lippy I can suck that up!
My extravagance is foundation, concealer, mascara (Lancome Hypnose though Rimmel the Falsies comes close for 1/4 price) but I've recently experimented with cheaper eye shadows- Revlon, Rimmel, would buy Bourjois if they weren't so sparkly, - and can't say I see any difference.