3 nights in Whittier is three too many IMO.. Stay in Girdwood and drive into Whittier in the morning. In May the 26 Glacier tour will be operating, and that's quite worthwhile early in the season - lots of floe ice hopefully.

The only drivable national parks then will be Denali, Kenai Fjords (boat tours from Seward) and - maybe - the edge of Wrangell-St. Elias (I doubt if McCarthy will be accessible but you can check.)

Homer has lots of accommodation availability of all types. I'd do an excursion across Kachemak Bay to Seldovia or Halibut Cove if any are running - very scenic.

IMO the best thing about Valdez is the drive there, past Worthington Glacier and Thompson Pass. Utterly spectacular.