TLDR: Heirlooms with 1/4 upgrade are perfect for your max level main can get pandaren enchants on those and mail those out to your alts. Maybe hold off fully upgrading everything until you get your pandaren enchants on the shoulders/legs.
So it looks like the best shoulder and leg heirloom enchants for levelling come out of pandaria and cost maybe 4k-6k gold each and can only be applied to heirlooms in the level 80-90 kind of range.
I don’t have anyone in that range on this server and couldn’t mail my enchants to anyone on the other faction let alone other server.
And the chainmail heirloom pants I had on were 4/4 upgraded, so my main couldn’t put the enchant on them either. So I started looking at a server transfer, but would need a faction transfer to get the enchant to an alt in the level range too.
Then I opened my heirloom collection to see if I had another pair of chainmail pants and saw that kilt. I never upgraded the kilt because kilts are dumb for all the jogging we do. Well it had a 1/4 upgrade on it, so I used it for something.
The 1/4 heirloom upgrade was perfect for max level main to apply pandaren enchants. My main pulled the 1/4 heirloom kilt out, dropped the 5k gold pandaren enchant on that sucker, and mailed it back to me.
5k not wasted. Rocking the +2 agility +3 crit in my pants… Pretty sure it scales up as I level…
PS for knowledge sharing> legion’s hidden satyr on your neck piece, and I think I put wod agility on my cloak, bfa crit on my ring and bfa crit on my weapon, and I think it was cata or northrend peerless stats on my chest. Someone had a trick about getting a common/poor ring for empty ring slot and drop a bfa enchant on that, but common/poor rings were like the 5-20k diamond rings and I settled for a 2 gold uncommon ring.