To chat or not to chat...
I understand your example, but I don't agree. :-)
Chat has a completely different "feel" to it than forum messaging. I enjoy both. In fact, it's much more convenient to do the forums. However, the enjoyment of chatting is a lot of fun. People will still post in the message forums as well as chatting in the chat room. I don't think there will be a loss of information as I believe you were inferring.
Ultimately, it's your call -- you are the one putting the time and money into this system for OUR pleasure -- for that, you get a gold star! I'm very impressed with the vBulletin system...someone spent a lot of time doing it right and making it look good. You've done an awesome job customizing it for our specific needs. Thanks! I ran a bulletin board system for 5 years back in the early 90's, back before the internet became so popular, so I know what it takes to maintain such a beast.
Anyway, if you are looking for opinions, I'd say adding chat would be a great addition.