We (my 16 year old twins and I--DH could not go) just got home from Eagle River in August, 2012. We met our oldest son there for his vacation.
Had a wonderful time. Our oldest daughter is married to an AirForce pilot stationed in Anchorage. We climbed a glacier, went river rafting in glacier water--brrr, went fly fishing for the first time in my life, went kayaking (first time ever), and I even jumped off of Mt. Alyeska in Girdwood, Alaska. I called my DH and told him that I was going paragliding (obviously first time) and he said, "You're not going to do that?" to which I replied, "YUP, I am!!"
It was great! Probably would not have done it if I didn't have an instructor on my back.
It rains in August in Anchorage...we hit the only week that the weather was sunny and high 60's. So I would suggest earlier in the summer. They have begun to have snow flurries up there now..
Must warn you that everything is expensive. I saved forever so that we could go and I am still paying for that vacation. We are hoping to go again next summer....this time DH is coming along. It will be the last summer that our daughter and family will be stationed there.
I would say "GO FOR IT!" You only go around one time so you may as well do anything and everything that you can. Start saving those pennies now!