I was too excited back when I first saw this place because I knew exactly what I was going to do with it. I agree 100% the item cap desperately needs to be raised, I just barely had enough room for the arena and dining/living quarters.... but i still have a massive back yard I cant do anything with because I'm at cap.... at least I will be ready when the cap IS raised by already owning the place. BUT anyways, I LOVE the Pinnacle. Its nice to be able to stay in one spot and "warm up" for Cyrodiil while awaiting everyone to join the group. It's also been quite fun to see 20 people chilling in the stands after a long day of fighting while groups of 2 work on experimenting with their builds and everyone watching gets to chime in and help out with ideas. Really feels like a true "Arena". Here's a little peak at what I did with it.
I bought it the day it was released - no regrets. My only gripe is there aren't enough furniture slots. 700 isn't enough to furnish this massive beast.