Having recently had the opportunity to "upgrade" to a 2007 Landmark, here are 3 things that I chose to add/change:
1. Dual pane window. We're hoping this will help reduce the need for a second AC in the bedroom. So far so good given the humid 95+ temperatures of the past week. Thermostat set at 78 and is keeping coach cool without AC running all the time.
2. Euro chair recliners with ottomans. Previously we had the bulky and cumbersome swivel rockers. The Euro chairs actually give us more "living" space since we don't have to pull them out as far from the wall. Plus, they are much easier to put in place for strap down.
3. Primary AC with heat pump. We ordered our prior coach with a second AC with heat pump, but it wasn't installed until early last fall. By them we had gone through the summer and several days of humid 90+ temps with no problems keeping cool and had decided we did not need the second AC. But after it was installed, we really liked the heat pump on cooler nights in the fall. I've already used the new heat pump and it did a great job of warming up the entire coach.