My mother is a big believer in doing all the tourist things, even in your hometown. Perhaps especially so. So, it wasn't uncommon for us to head off and see museums, the National Cathedral, or various other spots around town. And one time, she decided we should all do the Tourmobile, saying you shouldn't have to wait for visitor for the excuse to look like a tourist for a day. So we went (armed with a careful plan my mother had put together) and hit places that Tourmobile got us to a little easier than one could by metro or on foot.
I used a similar strategy in Barcelona travelling the Bus Turistic since it got to places like the Olympic Park that were outside the metro (or a very long walk).
Sure, I had wondered why there weren't other buses doing what Tourmobile did. And I see less of them these days. So I was sad to hear a combo of monopolism and the economy mean that the Tourmobile is no more. Sure, there are still plenty of ways to see DC (and it's environs) but, I'm still a little sad to see this one go.