Hi Cloudclipper, welcome along to the forums.
In regards to your upgrade question, as a 350D user myself the 400D doesn't look like too much of an upgrade to what we allready have, yes it has a few more nice features but no real "must have" extras IMHO. If your getting more wedding work then I would seriously consider the 30D with it's better build quality and features and keep the 350D as a back up. Dave's "spanner in the works" is a very valid comment as if you camera fails on you during the wedding shoot you cant exactly ask everyone to come back some other time when your camera's fixed!!.
One other thing is when you intend to buy, Canon is rumoured to be announcing some more new products at Photokina in a about a week or two, you never know what might be released
