Pandas alone should not be the reason to go to Chengdu (although it is obviously a great perk). Chengdu is one of my favorite cities in China. Assuming you haven't been to Sichuan, the food is amazing (and yes, hot-pot is that much better there). The Giant Buddha is amazing (but check on that, because I think they are doing massive renovations on it right now. Would not be fun to get all the way there and have it covered in scaffolding). And Dujiangyan is well worth a day trip. Chengdu is such a nice, green, easy-going city, especially compared to other cities in China.
The Pandas are great, but to actually get a selfie is very disappointing. It is very expensive, even by US standards, and you will quite literally get 30 seconds to hold it and snap one photo, not to mention you'll wait in an extremely long line for the pleasure.
I had a much better experience at the Chengdu Panda Base where, yes, it is set up like a zoo. However, go in off-peak and it wasn't crowded at all and you can still get very, very close to the pandas (and red pandas, which I don't believe the other locations have).