I feel long rides exclusively in my quads, should my calf muscles be doing more work? I notice a lot of cyclists with massive sculpted calf muscles, especially the kind that clearly ride as a life-style without worrying about minimizing body weight.

I've switched cities, and gone from a 7km round-trip commute to 25km round trip. I've been cycling hard as a hobby and often clocked 200km or more per week. After 6 months, I find that it's my quads that are getting larger, and my quads that are sore and tired after long rides, while my calf muscles feel hardly involved.

Does this suggest something wrong with my technique and/or posture? Should I be working to involve my calf muscles more?

Possibly relevant: I cycle with a pretty aggressive bent-over posture, on a touring bike with drop bars. I use clipless shoes and have been working on applying more power in the upwards-stroke. I ride with my seat relatively high, but comfortable and I'm certain I'm not over-extending my legs.
I don't think you have a problem here. Physiologically, your thighs are the engine room of your legs. They are designed for endurance and power and can keep working at a high output for extended periods of time.

Your calves are more for short bursts of power, such as jumping or sprinting. They can't sustain high power output for any length of time. In distance cycling, your calves should be fairly passive. Attempting to work them harder will probably just result in fatigue and injuries.