I have heard of the legendz series before (I still have to see what they did for the Korean versions), never heard of plaston gate and will have to look it up after this. Anyway yeah Legendz was skylanders before it was cool. To the best of my knowledge there are no emulator builds to handle them, mainly as I imagine they used some level of external logic which would also have to be emulated.
Otherwise the GBA was pretty basic -- no special chips or mappers like the SNES and NES, however there were a couple of on cart extras.
Still I did make a list of all the potentially trouble http://gbatemp.net/threads/buying-a-gba-flash-cart-in-2013.341203/page-18#post-4756995
Short version there is other than those handful of games with anti piracy (classic nes and later famicom mini titles if you must use them rather than superior emulation options, a couple of dragon ball ? games and maybe a couple of others)
A handful of games, most notably pokemon games named for gems, a couple of boktai games and megaman 4.5 have real time clock.
Boktai quite notably also features the solar sensors http://gbatemp.net/threads/boktai-solar-sensor-patch-kit.245127/
(read the whole thread)
Various types of tilt and gyro were observed.
Yoshi Universal gravitation/topsy turvy.
All of these are variously documented in http://problemkaputt.de/gbatek.htm#gbacartridges
and all should have Japanese releases as well.
Edit. Ah I see you are the same person that mentioned it to me a couple of years back.