Well, then your experience for Seward begs another visit with better conditions
In reality, Denali NP never closes. But the shuttle buses only operate May 20th until the 2nd Thursday after Labor Day. I flew up to AK one year when the road into the park was open to mile 29 in early April (that is the furthest it is open from when the Spring Road Opening opens it until May 19th). It was the earliest in years that the road was open that far that early. I drove the road twice each day - morning and evening. Saw some wildlife including a bear and cub. I also drove the road in the fall after the buses stopped operating and brought a bicycle. I biked another 10 miles into the park. That was great - I basically had the road to myself except for a few NPS vehicles and a contractor truck or two. I would go in the spring and fall again in a heartbeat, especially when the road is open to drive to mile 29. You could combine Denali with Talkeetna and even do a flightseeing tour out of Talkeetna depending on weather and availability.
Yes, will definitely go back to Seward another time. For this trip, I'll take the Glenn and Richardson to Valdez, then perhaps a drive up Parks.
BTW, ANC rental car at Hotwire is $7.50 per day, all-in total of $65 for 4 days. That's cheaper than a one-day rental in YYZ last year. Big difference.