Obviously, there are two different views on this matter. One is that having a balcony is the only way to do an Alaskan cruise. The other is that why spend the extra money when you can see more when topside, plus you don't spend alot of time in your cabin, plus it affords you extra money to spend on shore excursions, which is something you really want to do in Alaska.
Personally, we prefer the latter. The ship is not close enough to land during most of the time, so sitting on the balcony is really only worth it when coming into or out of port, or when sailing in the fjords. But when we were sailing in either of these situations, we were topside so we could walk from side to side and get pictures from both sides of the ship. When you're on your balcony, you only get one side to view from. And while you might be watching the scenery, you could be missing the whales breaching on the other side of the ship. But if you're sailing into Glacier Bay or Hubbard Glacier, the ship does a 360 degree turn so everyone can get to see everything.
We much prefer to save the money on the cabin and use it to purchase shore excursions. For example, we spent quite a bit of money on a once-in-a-lifetime excursion where we flew by helicopter from the airport in Juneau over Mendenhall Glacier, then landed on another glacier where we met our dog sled. We took a ride around the glacier for about an hour, then climbed back onto the helicopter to fly over a third glacier before flying back to Juneau. It was utterly amazing!!
There's so much to see and do that you really have to plan on spending money doing some wonderful excursions.
Of course, if money is not an option, then definitely go for the balcony.