Hello, new Zwifter here.
I am wondering if descending after a long climb adds any value to my profile/ experience?
Let’s say I climbed Alpe de Zwift in 80 minutes - is there any merit in “sitting through” the descent phase? Or will I just deflate my average watts in the ride?
Based on my current experience the descend is not realistic (pedalling or not same result, the avatar flies down the course).
What is your view? Ride down or end ride on the top?
Ride down - as a cool down and for low-effort XP 
In real life if I ride up a hill, I descend the hill as a reward for the climb (I don’t ask someone to come pick me up at the top of the climb, that would be silly). I do the same in Zwift. In my opinion if you’ve climbed a big hill you’ve earned the XP for the descent.
i have my trainer difficulty on about 5-10% at most so i just ride them. never been a fan of coasting, especially when the fan’s on and it’s cold
Low effort XP and distance, do it
You don’t have to sit through the descent. Pedal until you reach 57kph and get off the bike, go take a shower. You’ll coast the rest of the way down.