I have cruised to Alaska 4 times and never had a balcony. Yes, they are nice, but I'm not willing to pay a lot more for one. I'll be on b2b Alaska cruises on Radiance of the Seas in May 2017 in an inside (1st cruise) and an oceanview (2nd cruise). When it comes to cabin size on RCI - I'd rather have two inside or oceanview cabins for 4 people than one balcony cabin.
As far as RCI in Alaska - I don't think much of Explorer of the Seas' Alaska itinerary. It goes to only two Alaskan ports - Juneau and Skagway, plus Tracy Arm and a day in Victoria. It also sails from Seattle, which is less scenic than out of Vancouver. Based only on itinerary and not price -
DCL has the better itinerary of the two.