Are Charmonix and Wengen too similar?
They both are at the base of big mountains. One is German speaking and the other is French speaking.
The logistics of getting from Wengen to Chamonix and back to Zurich is certainly more complicated. 
Rather than Lausanne, how about smaller resort towns like Montreux or Vevey? If you decide to go that way, I'd prefer to take the big leg first and work your way back. Zurich>Montreux>Wengen>Luzern>Zurich. That way you can spend the last night in Luzern and go direct from there to Zurich airport as it is only 75 minutes on a direct train. 
Zurich airport to Montreux can be done in 3 hours with a single train change.