Just thinking out loud.
Currently when you close a board a user gets a message that the board is closed.

Why not still allow the user to view everything but disallow posting.

Are there issues with that thinking?

I realize that things may hickup if changing styles, etc.
But it seems to me when you close a board it is irritating to the user that they can't even browse the forum.

I usually only close the board when I'm doing stuff with the database - optimizing or repairing tables or whatever. In that case, I don't want 150 users and 50 spiders accessing the forum, even if they are only reading it, because I want to be the only one in there. I shut flashchat down, too, because it also accesses the database.

My users know that I only shut it down when I need to.

Understood. But that's why I mentioned an option.
Close board completely( as is currently)
Close board to posting only (new)

It couldn't hurt as an option; some people would like to do some backend maintenance and I think this could help for say making a backup where you wouldn't want new data inserted into the db... Simply have a "Read Only" mode.