well, a single charity delegate wouldn't contribute so much to inflation but could attract some new users that would come because they would be interested to be able to vote directly with their money to fund charities instead of corrupt bankers.
If the net amount of value that comes in due to a charity delegate helping with marketing exceeds the delegate pay, then it's obviously a good idea. Problem is, it's kind of hard to measure the actual influence of this on the influx of new users...
I would even suggest something like the EFF, as they fit quite a bit with the BitShares vision I think, and it would be nice to have a charity somewhat aligned.