Are on camera speedlight diffusers worth it?

Replying to my own post with a question:

I wonder if several speedlights, each with a small diffuser like the LumiQuest SoftBox III LQ-119 and placed next to each other could simulate a bigger light source. Each should be less likely to get blown over or destroyed by wind.

Thoughts? I'd rather not spend the money on more LQ-119's and find that my idea wasn't very good.