If you go to Gardner, the Absaroka Inn is a pretty decent place to stay. All the rooms overlook the Yellowstone river. Of course, you also get to see the "beautiful" downtown Gardner area, but the rest of the view is fine. When I asked for restaurant recommendations, they sent me to a little place on the second floor of one of the downtown buildings. Certainly not fancy, but I got a huge chunk of very good prime rib for a remarkably reasonable price.
As mentioned by someone else, Mammoth Springs is nearly dead, and wasn't worth the climb up many stairs to see. Darn shame, since I remember it from the '70's when it was amazing.
Chuck
Just thought of something we considered for a future visit....if you're planning to stay a week or so, you might find a deal on a cabin near the park. We saw some literature on cabins while we were in Gardiner, and having kitchen facilities would make some of them a pretty good deal vs motel rooms and restaurants for every meal. Lots of good regional beers in that area, too. Guess that shows my interests, huh?