I think your revised schedule is quite doable.

I wouldn't worry about a glacier cruise in Whittier if you're doing the ferry. The ferry won't take you up to the glaciers like the day cruise will, but they do get within sighting distance of Columbia Glacier (and if you have a nice captain, he may take you a bit closer to Columbia Glacier than you would normally go), and you'll likely have seen glaciers on your day cruise in Seward. That said, don't expect to see tons of glaciers on the ferry ride.

Also, Google Maps suggests equal driving times from Copper Center to Healy via the Denali Highway (Paxson to Cantwell) as the Glenn Highway to the Parks Highway (via Palmer/Wasilla). Don't be fooled, though: the Denali Highway is a LONG drive through a VERY desolate region. You're not likely to pass more than a few cars going the opposite way through the entire stretch. It's also on the restricted list of roads from every major rental company, since it's not paved and the chance of damage is far likelier (and you're in for a VERY expensive tow bill if something happens--that is, if you can even get ahold of a towing company, since there is NO civilization and NO cell phone coverage on the entire stretch of the Denali Highway). Due to this, I'd definitely plan on going a lot slower than Google Maps suggests, making the Glenn/Parks a much speedier and safer alternative. That said, it is a beautiful drive through a desolate moonscape and is an awesome introduction to the raw wilderness of Alaska. Just be prepared--know how to change tires, bring a can of gas, and have blankets and emergency supplies in case you do get stuck.

Oh, and yes, I think the short detour to Talkeetna is worth it, if just for the kitschy factor and the chance to see a real Alaskan mountaineering town in action. (Watch for the numerous flights taking off with people bound for glaciers and base camps and all that!)