Reduce engine wear?!? IF you can find one, please post [a link to] even ONE engineering study that quantifies the reduction in engine wear.
Once you get about 10% below max rated thrust, incremental reduction of engine wear is miniscule. Engine speed and EGT which are the main drivers of wear -- are already significantly below max. In fact, on the 744 and 748 we too often take off with thrust set SIGNIFICANTLY below climb thrust! That is simply a beancounters' exercise to reduce engine lease payments, and has NO operational value.
I agree, the first few degrees of flex save the most on engine-wear. After that it becomes a paper excercise. On A320 we also see flex N1's that are below climb thrust. Thus increasing the fuelburn to altitude even more.
The most efficient climb (zero-wind, ISA) is at maximum thrust straight op to optimum cruise, if you reduce thrust in the climb you burn more fuel.
The reason for flex is thus engine-wear, and at higher flex temps it's just a beancounter paperwork excercise that actually increases real term costs. But those costs are handed to the engine-lease companies, so the airline still saves money.
It's probably a bit more complicated though, as some engines can also be de-rated and then use flex temperature on top of that. So there must be a bit more to it then the simplified version.