Tom,
NO more agony necessary. I really think you will find the following system as the best overall compromise for your vacation needs:
Contax 645 w/ grid screen,WLF,prism,55, and TLA200.
Your walk around/daily setup should be: WLF and 55.
When you need to add flash, then swap out the WLF for the prism. It only takes about ten seconds. When not in use, the prism is only a little extra weight, but can squeeze into small spaces in your pack (like vertically).
I don't think you can get any more quality per gm. This is a VERY small and lightweight travel kit for MF quality.
If you still need more rational justification to ease your mind, you can also think about it this way. You traded off the luxury of the zoom, to get the benefits of the prism and flash (roughly a wash in weight and size). This is a great compromise.
Just take this setup and don't think twice. Enjoy your family and vacation and the photographic memories.