Can't speak for everyone, but I think a tour without the JSA is basically a waste of time. Dora Observatory is only worth the time if the weather is clear. The tunnel is a decent hike if you walk out, but otherwise pretty anticlimactic; Dora station, if they take you there, is nothing special, and the cafeteria lunch you get at the border facility (where the ROK-bound trucks are X-rayed/scanned) is a wasted meal, IMO. Maybe Imjingak is interesting the first time you visit, but not all DMZ tours get you there.

Personally, knowing now what I didn't know when I scheduled a DMZ tour (which included the JSA), I would pass unless I can get to the JSA.

I think you'd be far better off spending time on something which interests you more.