In my opinion, a balcony in Alaska is as close to a "must" as you can get! The vistas are so magnificent that it's a shame to miss a single minute of it. That being said, I should explain that my husband and I love wildlife and nature. So mountains, glaciers, whales, etc. are our main interests. We would skimp on the excursions to see the nature (except we would splurge for the White Pass Railway in Skagway).
Yes, we spent time on the decks, too. But like Dave said, it can sometimes be difficult to get good spots on glacier day or when coming in to the ports.
All I can say is you will love Alaska no matter what you choose. We've been there twice and hope to go again in 2013.