Sin'dor
Veteran
Nice catch! (I did notice that on my initial read-through, then completely forgot about it by the time I'd finished typing...)F2Ps/20s can enter Gnomeregan by walking into its instance portal. Alliance can enter the instance located around here, while Hordes enter the instance through a engineer portal (engineering is not required to use) located at Grom'gol Base Camp in Northern Stranglethorn (and Hordes can get to that base through a blimp at Orgrimmar).
You can see just how dungeon-boss-loot will "scale" by checking the in-game Dungeon Guide... Gnomeregan boss-loot doesn't come down to lvl-20, but because it "Binds when picked up" you still get the "transmog" appearance (as you mentioned).[I haven't checked yet if scalings have affected this or not, so I don't know if this trivia is still relevant or not]
The trash does occasionally drop equipable gear, but it depends on what type of item it is. When I was soloing it last week I had a Jagged Star drop (that I equipped for the transmog), as well as a one-in-sixtyfourthousand Shield of Thorsen drop (which had my ProtPally pretty excited for the split-second it took me to realize I couldn't equip it).
Appreciated... and to show my appreciation, have a chicken-fish that isn't so damn "dark".+1 for the addon.