Waluigi will always be the one with the most character and that's a FACT. Waluigi will get his own game and series when I get into video game designing. Trust me on that. And Waluigi will be more active in Wario's games as well.
I believe that him not being in Mario Kart 7 was the start of the beginning of Psycho Waluigi. Because in the intro of Psycho Waluigi he is traveling in his Hot-Air Balloon and we all know what happens.