We did the tunnel and Dora Observatory with a private guide*. We really enjoyed it and thought it was well worth the 6-ish hours. I would be shocked if the JSA re-opens anytime soon.
* - because we weren't part of an "official tour group", we had to go to the Imjingak DMZ village extra early so the guide could stand in line for first-come-first-serve tickets to be let into the DMZ. It does give you time to walk around a look at the sculptures.