I haven't shown the room in a while, so here's an update. It's now a functioning office, although we still have a lot of work to do to finish it up. The ugly door and window are slated to be replaced professionally in the near future, and we have lots of molding to put up and other small touches.
One thing that made a surprisingly big difference was re-staining the paneling. We had to stain the areas that had been hidden by the old drop ceiling for years, and we found a color that was close but not a perfect match. So we ended up redoing the whole thing, and I like it much better now.
For comparison, see this previous post.