You asked a simple, direct question: What town on Cape Cod, could you and your husband go next summer, drive to your accomodation, park your car and walk to beach, restaurants, shops and attractions.

Three towns on the Cape match your criteria to varying degrees:

Provincetown has the most accomodations, shops, restaurants and nightlife right on Cape Cod Bay and all within walking distance of each other. You can, as you desire park and walk to all of the above without using your car for your entire stay. If the bayside beaches are not to your liking you can hop on the trolley to nearby Race Point & other National Seashore beaches. Please do not discard this town as a wonderful place to visit, because of a few homophobic Fodorite posters who insist on informing you how "gay" Provincetown is!

Chatham is a very scenic area but very expensive for waterfront accommodations. A few of these inns are fairly close to town but the majority of the inns, motels are not accesible except by car. If you can afford and reserve a place such as Chatham Bars Inn, the town is still a bit of a walk, and there is a lot less available then in Provincetown.

Hyannis, has the most choice of accomodations, restaurants, beaches, nightlife etc. but here you will need a car to get to everything because it is all spread out.

Just thought I'd throw in my vote for Falmouth. It has a lot to offer - many beautiful beaches (some on Buzzards Bay, some on Vineyard Sound, water is warmer than National Seashore beaches)a lovely town center complete with a village green surrounded by beautiful historic homes and churches and many nice shops and restaurants. There is also the scientific community in quaint Woods Hole, not to mention easy access to Martha's Vineyard. And - you can certainly accomplish your "walk everywhere goals" - to town and to the beach from several inns and motels in the downtown area. I think you'll like it - I know I do!

I have to agree with those that said Chatham or Provincetown. We went two years ago and regret not staying in Chatham. It was by far the most picturesque and what I thought we would find on the Cape. I absolutely loved Provincetown (I am not gay). I found it lovely, interesting and never a dull moment. Take a whale watch cruise from here. We saw 10-15 different whales when we went out from here. I can't remember the name of the cruise, but it is the only one that has a guy speaking from the Oceanographic Institute. The only thing I should warn you about is the lack of air conditioners in the hotel rooms. If you want one, be sure to ask when you make reservations don't just assume that one will be in the room. If you are going in July, you will need one. The temps hit high 80's and into the 90's when we were here.
Good luck and have fun.