Brant, your experience tracks well with mine although I only use CL.

I agree about selling early - I lucked out in selling both my 17-55/2.8 and 24-105/4L before the prices fell significantly.

In terms of 'investing in exactly what you want', as a general rule, if it's a lens that I know I want, I'll buy it new. But if it's a lens that I'm interested in but uncertain if it will become a long-term part of my kit, I buy them used to begin with. When considering lenses that I've bought used then subsequently re-sold (about 6 lenses in total), I've actually made money on those overall - enough to offset what I've lost selling lenses bought new (e.g. my all my EF-S lenses). I'm still at ~75% return on sold gear, due to camera bodies losing significant value.