Quicksilver is an ok company, altho some of the departures are cattle calls with hundreds of divers/snorkelers aboard. My absolute fave for daily trips is Calypso out of Port Douglas, with terrific dive masters & a long history of small groups (no more than 20 as I recall). http://tinyurl.com/2hn56

I've dived with Calypso's skipper/divemaster for 15 years. I never get tired of the Skyrail to Kuranda. Floating above the canopy is a real treat (take binocs) & stopping at the 2 change points for the short naturalist talks is well worth it. For some hard work in Cairns, take the trail to the top of Mt Whitfield near the Flecker Botanical Gardens. It's an isolated enclave of rainforest, very popular as a locals workout, & I've seen all kinds of wildlife up there. It's only a 5-min walk from my house, so I go every day! Eclectic dining, Oz-style, is to be had at the Red Ochre in central Cairns.

Cairns is flush with bike trails, so renting a bike & pedaling down the Esplanade, up past Mt Whitfield & the Gardens, thru the central swamp (it's a park) & back to CBD makes a fine afternoon.

If you want a wilderness experience, I can't say enough good things about Wilderness Eco Safaris, a 4-wheel drive look at some very private & wonderful rainforest. http://tinyurl.com/5e8kb

There are lots of 4-wheel drive trippers out there, but Steve is very eco-conscious. Max 6 per trip.

OzExperience does cater to younguns, but people of all ages are welcome. Some of their bus trips up into the Daintree are with too large a group for a good wilderness experience (see above), but if you want to get up to Cape Trib, it's an option. Certainly for the route you're considering, it will be good fun. Gail Back in Eugene after another dash thru the Palouse