Hmm that does sound interesting. What dungeons do you run at 20 again?
If you random, you will get: Deadmines, Shadowfang Keep, Blackfathom Deeps, Stockades, and Wailing Caverns. Some Best in Slot items come from those dungeons. Sometimes you can get a group of 20's together and go over to Gnomeregan for chest drops and hunter scopes (the rest of the drops in there require 21 and over to use). A surprisingly low number of heirlooms are BIS, depending on your class. I play a resto shaman, and my only BIS heirlooms are the mace and robe (I think). For most of your gear, you try for dungeon drops and hunt down chests for rare drops like the coveted Magician's Mantle. Then you play WSG and AB, gathering honor for heirlooms. You can also do Darkmoon Faire stuff and buy an heirloom or two with those tickets. The biggest community for this is on Aerie Peak, where I play. Queue times for BGs are typically around 5-15 minutes for WSG, and 50 minutes to an hour for AB. However, joining one BG does not kick you out of queue for the other. So you queue for both, usually get in 2 WSGs before AB is ready.
Also, players for whom the Rifle Commander's Eyepatch (Stockades quest reward) is not a good match all go to the STV fishing tournament, and try to fish up the rare fish that gives you the Lucky Fishing Hat as a reward. This is the BIS helmet for many level 20s.
It's surprisingly fun. I didn't expect it to be when I got bored and made a free account a few weeks back.
Edit: You'll also want to download the f2p addon (just search f2p in curse), which contains a (legal) workaround that will allow you to talk in the f2p chat channel (f2p players cannot normally talk in public channels). This allows for easy chat and grouping with other f2pers when you want.