That's actually a pretty clever idea you did.
I'm sure you won't want to hear this though, but I say leave it at that and move on with the game. If you start to imitate the campy-but-fun encounter you did, it'll ruin the originality of the first encounter and it will just become campy (without the fun). That's what producers do...they get something like a funny commercial on their hands, people love it, so then they grind it into the ground until people think it's eventually lame (Budwieser frogs, Geico lizard, Burger King King, Geico Cavemen, ect ect).
If you like them so much that they gotta appear again, rather than make imitation scenarios, have them make cameo appearances throughout the campaign that are completely different. Obviously they are a batch of quirky goofball-like guys. So play off that, but don't have them continue to disguise themselves as scary creatures and make a gimmick of that.
Instead, run them as oddball side quests encounters. One idea could be:
Early on, commoners have told the PC's of some recent bandit raids on the road. The bandits lure travellers by pretending that one of them is a girl on her pony and she's lost on the road. When people stop to help her, the bandits cast sleep spells & rob them. So while travelling, the PC's find a wagon that has been destroyed. Get the PC's to realize that giants (or whatever) may have just recently taken captives from this wagon (footprints appear to be small children) and hopefully the PC's will want to rescue them. The giant tracks lead off into the woods and to a cavern mouth up on a hill. When the PC's scout the area, they find those same Gnomes piled into a cage with the gnome leader dressed as a girl and nervously dancing on a giants table trying to entertain the giants. The scenario is that these Gnomes are the bandits (those weren't children tracks), they have been captured, and the Giants are forcing them to entertain them before they eat them. Now the PC's get to rescue these Gnomes and the Gnomes deny being the bandits...then have them escape.
I say keep making the Gnomes appear silly in ways other than impersonating monsters. Keep changing it up.