My experience, starting with 5 spd FW and now with 11 spd cassettes is that once you have worn out two chains
the FW/cassette will object to the 3d chain and need to be changed. When the 3d chain wears out, chainwheels
get to be at or near EOL, more so with 2x than 3x. Unfortunately with SRAM/Shimano/FSA and some others
price of a pair of new chainwheels is such that it makes some sense to just get a new crankset for not much
more.
It depends on how much you favor a few cogs. I ride cassettes with one tooth jumps to the 19T, don't neglect any apart from the small cog, and have 25,000 miles on my current cassette that's on its 6th and probably last chain.
It also depends on how worn you let it get which depends on chain metallurgy. I run Campagnolo chains with front shift degradation from increased lateral flexibility as they reach 1/32" of elongation around 4500 miles. Wippermann chains reportedly grow slowly too.