Urbanna is definitely a good place to keep the boat. However, Deltaville gives you more sailing options: up the river towards Urbanna, mouth of Piankatank, the Bay. Plus you will have a good choice of reasonably priced marinas.
I stayed in Urbanna for a few days in September and had a great time. Whether it would suit you for a basing your boat there would depend a great deal on how you use your boat.
Urbanna is a long ways from the Chesapeake, but there is plenty of sailable water right outside the entrance to the town. The East and West Branches of the Corratoman would be an easy sail as would the anchorages in Carter's Creek, so there are some quick overnight trips available without ever entering the Bay. That said, it would be a looonnng haul to say Onancock and even places like the Great Wicomico or Fishing Bay would be a pretty good day sail away.
All in all though, I think I'd agree with Dog8It that Deltaville would be a better base of operations. I think I'd go further and say that the Broad Creek entrance offers the most possiblities allowing visits to the previously mentioned anchorages (but now adding Urbanna as a place to visit) without having to enter the bay, or if the weather was agreeable any of the many creeks between Windmill and Smith Points or going around Stingray point into the Piankatank. You can still do those trips easily from the Piankatank side, but it would require heading out on the bay to get to the shelter of the Rapp. which might limit you to a daysail or anchoring out in Fishing Bay/Godfrey Bay on a few occasions a year.
When we sailed from Deltaville, I always liked that I had fairly sheltered places I could sail from Broad Creek, even when it was blowing stink out on the Bay.
Edited to add, we had some dockmates that went to Tides Inn almost every time they took their boat out, because their sailing buddies were based out of Urbanna and Carter Creek was the only place they could manage to meet up. The friends moved their boat to Deltaville taking our old slip so now they can choose other destinations.