You ask some good questions!
I think the answer to your first question is that I own two VX2100s. I'd rather have two 170s, but budgets are a fact of life. I'd much rather have 2 2100s than 1 P170. I bought a Beachtek adapter which lets me use XLR audio. I can have 2 @ XLR or 1 XLR and 1 Mini. The Beachtek is also a mixer.
As for the FX1 - I have reservations because of editing hardware and software issues that I'm a little unsure of, but that is one mean-looking camera and clients love mean-looking gear (actually, so do I). I'd love to have an excuse to buy an HD TV and since HD is the future, I feel a certain obligation to offer it to my clients.
But, honestly, other than HD, the camera is less well suited to wedding videography than the VX2100 mostly because of the 3 Lux rating which concerns us a bit. Also, I've read that HD is more difficult to focus for also, and quick, manual focusing on the fly is important in good wedding videography, or any event videography for that matter.