While people seem to think that tourism to Alaska will be big this year for the reasons you cite, the cruise companies recently have been announcing locally that bookings are down and Juneau should expect a down year.

Regards Andrew's comment about the sun never going down, you have to go up inside the Arctic Circle for that, visit Barrow, Nome, Kaktovik, etc. BAsically, it depends upon what you like and have experience with as to what type of trip you want. I'm not much a cruise type person but they are certainly right for a lot of folks.

Re: the comment about not being able to see the northern lights in the summer, depends upon where you are, I've seen the northern lights in the summer here in Juneau quite a few times actually, of course we have to get a clear night for it and that doesn't happen to often here.
jerry