I would also avoid the watered down ports, but I only found this to be a real problem on the original GB. The ports were probably some of its best games, but I have no incentive to play them as I already owned superior versions on the NES. There are great exclusives on both the GB and GBC if you are willing to seek them out.
Ignoring the GBA, however, is criminal for a gamer. I've heard a lot of people complain that it is nothing more than a platform for SNES ports, but it has some of the best exclusives I've ever played. For example, I only keep games that I feel are absolutely indispensible and can see myself coming back to and I have just as many GBA exclusive games as NES, SNES, PS1 etc. Do yourself a favour and get into the Castlevanias, Sonics, Minish Cap, Pokemon, Golden Sun plus the ton of more obscure stuff available (Ninja Cop, Drill Dozer, Densetsu no Sutafi, Lady Sia to name a fraction of it). It's one of the best systems ever made and that's not a claim I make lightly.