GGeorge: From our experience we didn't enjoy riding all the way to Wonder Lake. All the animals were seen from the park entrance to Eielson Visitor Center. We stayed 5 nights at Teklanika campground and purchased the TEK Pass. The bus stopped all day long at the campground and we were able to ride as often as we wanted for how long we wanted and once we did take it to Wonder Lake. If you wanted to get off and stroll the road for a short time or take a walk up in the tundra we did and caught the next bus coming by. You can't believe the peacefulness once the bus pulled away. We were alone in this vast wilderness - absolutely breathtaking.
For Teklanika campground and purchasing the TEK Pass we only did so about 3 weeks prior when we could better judge when we'd get there...many things can happen along the way. Also, we used the school bus tours rather than the more expensive luxury tour bus tour which gave you a box lunch. We brought our own cooler. Our bus drivers were well experienced at spotting the animals and they would stop for us to take photos. They also gave us good information as we drove along.
As it turned out we got to the area early so on a whim we boondocked at a lovely spot off the highway near Denali and early the next morning we drove into the park and easily secured an additional 5 nights in Denali's front campground, Riley Creek with our 40' motorhome. There is so much to do with ranger programs, ranger hikes, looking for critters at all times of the day, that we easily filled the additional 5 nights.