I love the huge roster in Tekken because it gives a player a lot of options as to who to choose as their main. Nina and Anna could be perceived as very similar characters but a fan of the series who knows his/her stuff would know that they're very different to play as and against. Ditto Armor King and King. It's clearly a formula that's worked for Namco, anyway. Tekken 3 and 4 both went with smaller rosters but Tag, 5 and 6 are renowned for being the better games of the series because of the large number of characters. Namco are always constantly working to make the more similar characters more different with each installment. Lee and Law used to be identical but you wouldn't know it now. Bryan was supposed to be Bruce's 'replacement' but is now much more of a big hitter as opposed to Bruce's high-low mixup dependance. Cassandra is worlds apart from Sophitia now in the Soul Calibur series too.

So, no. I reckon you can never have too many.