LG....we have done it....it was wonderful, small plane, great pilot, lots of info on glaciers we flew over, and the area. Coming into the area was beautiful, lots and lots of eagles (saw mating ritual); bears; great, great meal; waterfalls, wild blueberries all over, nice trail thru the temperate rain forest....Well worth the $$$.
That said, you have to do the whale watching too. We do it every time (4th trip coming up in May!)....we have done it in Seward, Juneau (twice)...used Allen Marine tours every time, always saw lots of wildlife and whales...the best ones however are in Seward (if you are going there)...because we saw lots of my favorites there, ie. sea otters and puffins!
Have a great trip!