This is exactly my approach, go in with low expectations. For my September R/T SFO-MEL I'm taking along some PJs from previous flights in F with a choice of LH, NH, SQ, TG, BA offerrings currently sitting in the original unopened packaging. Prefer these to the last time I tried the UA PJs on the MEL-LAX flight; felt cheap and synthetic (was there any cotton content?). Just for fun I'm trying out a used set of SQ F PJs next week on the SEA-SIN flight in J; cold wash and air dry seemed to work, but I'll know for sure when I get onboard the flight haha...
Cheers,
-Cyborg