Add another character (species)

I have been considering adding another character to the game for some time. The original design included seven species, but at some point during this project I decided that simplicity demanded a dramatic reduction in the number of characters, so I brutally cut it down to four characters -- and therefore four species. However, after mulling over the issue for months now, and seeing how the game is developing, I have decided that four characters is not enough. The overall complexity of the design comes from both the number of characters and the number of verbs, and I'm finding that there aren't that many verbs, ergo the need for more characters. But what is the right number? Should I take a little step up to five? Take a bigger step up to six? Or go all the way and restore the original seven species? I rather like that idea. But is it too many?