Even if we weren't hikers, I couldn't imagine spending only one day in Glacier National Park. We have been to the park in 8 different years - the first, 1992; the last, 2013. We spend a total of 17 days at the park in 2012 and 2013. 1992 was the last year one could drive an RV from one end of Going-to-the-Sun road. A very scary drive. We drove back around on Hwy 2 instead of traversing the park road twice!
The bus tours may be worth the money; certainly if you don't have a toad. But there is much you want see, even if you take the most elaborate of the tours. For example, you wouldn't get this vista
(You would get a stop at Wild Goose Island overlook. But to get this view, you would have to go to Sun Point.)
Some of the tours go to Two Medicine, but not all. Some of the tours start at Many Glacier, but if you are not staying there, the tours don't take you there.
There are many non-strenuous hikes, for example:
Running Eagle Falls - 0.6 miles, elevation gain of 15 feet.
My advice, spend as much time there as you can afford. Oh, don't forget the ranger lectures in the evenings. You will learn fascinating things. (Who knows why the road is on the southeast side of Lake McDonald instead of the Northwest side, where the views are much better?)
Tom