These 320gsm tops seem quite durable, i've had hit and miss results varying with brand, Tog24 200gsm tops lasted over a year so far but the pants that went with them were holed at thighs and buttocks within 3 months and useless after 6, trekmates 200gsm similar, my previous On-one 200gsm tops are still going strong bought in feb this year.
I used to wash all my woolens with nikwax wool wash on the wool cycle in my machine and dry them on hangers after reshaping but i was never fully pleased with the product and sometimes had to do a double wash to get them smelling normal again and once dry there was no scent on them at all, i recently bought the kookaburra wash from On-one and it is much better including for environment and leaves them smelling real nice even days after the wash and dry when i get them out my drawers, again this is used in the machine on the wool cycle, i wash all my woolens together including my angora and cashmere beanie hats and pure wool ex army sweaters, works out about once a week in one big woolwash