I've been collecting Super Famicom and Handheld games in Japan for the last year and a half, and I've bought a Game Boy Pocket (original game boy color scheme, speakers are busted but it cost $3 and otherwise looks great) Clear Game Boy Color, Anniversary Game Boy Micro, and Super Game Boy 2. As usual with any hardware I have bought, I didn't see any SGB2s for a while, then I bought one and immediately started seeing them everywhere for half the price I paid (this happened with NGPC, paid $20, could have seen them as low as $5, just bought a famicom, my favorite store got A/V famicoms in, etc...).
I was on the fence about getting a copy of Castlevania: Belmont's Revenge for about $16, since I assumed it would come to the 3DS eshop for much less and that would drive down the original price, but the store that had it sold out, GB games aren't really releasing for the VC anymore, and I haven't seen it in any of my local stores, only some in bigger cities where it's more expensive.
I bought the GBC mostly to play Kirby's Tilt and Tumble, since that won't work on any other system I have, but I do kind of want to rebuy a classic GBA (traded my original in for an SP). I may also get a DSlite (only have a DSi right now, gave my DSphat to a nephew before I started collecting handhelds) so I have something with a bigger screen than my Micro that plays GBA games and looks great. I'm really disappointed that the SP+ never made it to Japan, as that's what I really want.
I HAVE picked up:
Warioland 2-4 (have 1 in the US still)
all of the GB and GBC Kirby games except Dreamland 2 (I used to own it and grew to hate it)
Bonk GB collection
Alleyway
Cattrap
Penguin Wars
Batman
Yoshi's Panel de Pon
SaGa 1
For Frog the Bell Tolls
Megaman 5 (Rockman World 5)
Megaman Xtreme 2
Solomon GBC
Mother 3
Fire Emblem 6
Starfy 1-3
Suikoden Card Stories
Klonoa 1,2, and Heroes
Mr. Driller Ace
Wario Ware: Twisted