Heirlooms are somewhat nice to have gear in all of these slots always up to date since quests aren't the greatest if you don't do sidequests or do older shit(cata items are fucking trash in the standard leveling iirc), but yeah they're not worth investing any money to upgrade them unless you're bored.
I don't think Azeroth autopilot was updated yet but they're working on it, so they might have something, if only just one expansion's path, which would probably be WoD if they don't rescale shit. There were quite a few bugs in alpha with the leveling though, like NPCs you get in quests don't scale properly(they one shot stuff) and sometimes you get quest rewards that aren't scaled down(I got lvl 52 blue gear from quests at lvl 25ish) and it felt very unfinished. The expansions are poorly balanced and it seems they're not doing fuck to fix it before prepatch, so it's possible they'll slap some random nerfs on shit to slow down WoD and make it complete ass because they overdo it.