I mainly travel for leisure (and my company policy is to fly on the cheapest flights, so they are usually scattered around OW, DY/D8, *A and SkyTeam). I don't like flying that much that I would do mileage runs, but I'm willing to choose holiday destinations which offer good mileage for a reasonable price and I might take a detour if it increases the mileage.
Last year I did 3 long haul round trips in paid J and that was quite easy with the amount of annual leave we have in Finland. One of them was to CAN (bought at 1099 e in a sale in 2017),one to BKK (1199 e) and one a cheap QR business ticket to AU (which are not around anymore). CAN was a good destination for taking an onward flight because of the vast network available from there (mainly on CZ). There my actual destination was Japan and I flew via CAN just because of the points (but on the way back it required an overnight in CAN).
If you prefer destinations in the US, then I guess the primary options of getting good mileage are business tickets ex-ARN or Value tickets ex-MSQ/LED/SVO (but from LED and SVO the Russian visa adds to the cost).
However the strategy of cheap long haul J trips doesn't work that well once you are Plat, because you have to spend your upgrade vouchers somewhere. You'll have to add at least one long haul return in Y to spend the long haul vouchers, and also a second one if you don't have use for the European vouchers.