I used to overspend a lot when I was using Canon, the L lens are addictive. After switching to Pentax, I spend 50% less, reasons are
1. Not a lot of lens choices to buy. (this will change since Pentax announced so many lens this year dammit !)
2. Not a lot of lens FROM the local shop that I can buy. (blessing in disguise if our local distributor is not bringing in 1/2 of the new lens being announced !)
3. I always looking out for cheap lens, because I don't want to spend too much on a single lens anymore, no justification at all.
Even my wife helps me in clearing my doubts when I buy a lens, she will ask, "Are you going to use it often or just gonna be collecting dust in the dry box ?" So this will impact my decision and help me clear my doubts also.
Since most of us are not using our gears to make money, there is definately no justification for return of investment (ROI). So my only comforting thought is that, this is an expensive hobby. Some people spend tonnes on their cars, some on aquariums with exotic fishes etc. So don't regret of what you have bought, if not happy, then sell your purchase 2nd hand, that will make someone else happy also.