Honestly, mass emails to all registered members is not a step to be taken lightly. There are over 4,000 registered members here. I would assume that at least 80 percent of those email addresses are no longer valid. So I would get a ton of messages bounced back to me as undeliverable, flooding my inbox. And some mail services (yahoo, hotmail, gmail, etc) will make note of a large number of bounced emails and assume that the source (me) is a spam bot, then block the site and IP address)
Heck, if I remember correctly, one of the members requested that I set up the chat. So I did so. Far as I know, he never used it afterwards and has been long gone from here.
I really hate to sound negative to these kinds of suggestions, but I have been through a lot of this stuff already in the past and experienced first hand some negative consequences that aren't readily apparent beforehand. I certainly don't know what is needed to turn this site around, but I have seen things that could quite likely make matters worse.
So if someone wants to take the bull by the horns and try to drum up enthusiasm and participation in the chat room, then by all means, give it a whirl. If I feel the participation in the chat is robust enough to be a selling point to invite long absent members back, then I will consider bearing up under the headaches that would be caused by a mass emailing.