Glad to see you're headed out to Colorado for a bit, it's absolutely gorgeous here. Are you renting a car? Depending on when in June you come out, there are several fun festivals going on in some of the cities you've mentioned.
Yes, go white water rafting, it's a blast, particularly stretches on the Arkansas River. Garden of the Gods is definitely a must see. Ren's suggestion about Air Force Academy is a good one too. While you're in the Springs area for those, you can also hit up the Olympic Training Center for a tour if you guys like that kind of stuff.
I mainly know the Colorado Springs area, but if you want a nice place to dine or golf, you can check out The Broadmoor (just hosted the Women's US Open last year). If you're staying overnight in the Springs, I recommend either the Broadmoor or the Antlers Hilton, both are very nice.
Buena Vista is a pretty small town and I don't know of any particular places that stand out for dining and site seeing there, besides the rafting.
There are more fun rafting and zip-lining tours out of Canon City.
If you two like fishing, there is a ton of great fly fishing out here...highly recommended.
Cripple Creek is a fun, old mining town high in the mountains with a bunch of small casinos. A lot of my friends take their family members there for a fun day of wild west gambling.
And don't forget to swing by the high security prison, in Florence, it's beautiful. Okay, maybe I'm joking on that last one, lol.
If you want more suggestions as far as Aspen and Denver, I am happy to contact my friends up there to get some more specific info for ya. Just PM me.
Hope you get to enjoy the outdoors here as much as I do.