And the answer is YES, it does make a big difference for a guy that weighs 220 pounds.
However, after reading forums like this one, I was not quite sure. People recommended against it, suggesting that it really doesn't make that much of a difference. But then again, a lot of people that are posting are "normal" cyclists that don't weigh a lot.
My problem was that my Bianchi Vertigo carbon bike was communicating every single bump on the road, resulting in a high-frequency vibration and punishing pounding of my rear end even during short rides.
The problem became even more obvious after I bought my second bike, a 2014 Specialized SL4 Roubaix. There was simply no comparison in the ride quality -- even with the same tires, saddle, and tape. Yes, I do realize that the frame makes the world of a difference. But the difference was a bit too stark IMO.
Getting 700x25 Continental Grand Prix 4 Seasons tires and experimenting with tire pressure didn't make that much of a difference. Playing around with different saddles didn't make a difference either.
Finally, I decided to pull the trigger on a carbon seatpost. After some research, I settled on FSA SL-K due to good reviews and a special I found on BikeWagon for $58.49.
I had very low expectations, fully expecting to return it. But the initial ride changed that mindset in a hurry. This seatpost had almost completely cut out high-frequency vibrations, transforming my ride into not just bearable, but a really enjoyable one. Now it feels like a completely different bike. It got very close to the feeling I had during an extended test ride of 2014 Trek Domane 4.7 last year.
So, very positive initial impressions. I will update this post if something changes.