Also, how was the appraisal done? In some cases the appraiser only looks at the house from outside, without stepping in.
If you are planning to sell, market value is determined by what today's buyers are willing to pay for similar property. You'd need to talk to an agent about recent sold statistics, and a good agent would be able to go through them with you, explaining why one sold for more than the other, and where your property is in that equation.
Some properties are unique, and comparison to others on the market is not that easy, but it can be done. It might also take little more time to sell, because you'd be looking for a certain type of buyer who would appreciate all that this unique property has to offer. In that case, marketing should be adjusted to create an extensive internet exposure, to catch most wide pool of buyers. (say, relocating buyers who are currently still living in a different state and can only search MA homes online)
I think that the others gave good advice - there's no blanket answer - just get a comparable market anaysis or, if you want more certainty, pay an appraiser to estimate the value. The appraiser will visit the home and make note of any features that could adjust the value.
A real estate agent will be able to guide you on the "highest and best" value of your home for sale. If you are thinking about selling your home, please do give a real estate agent a call. Many agents will provide a free and no-obligation market analysis and will also advice you on the things you can do to obtain the highest value.
Keller Williiams Realty
I think you get an idea of what is the plus value of dead-end street and waterfront. But there are a lot more to be consider when real estate agent evaluate the market value. Size of the lot, shape of the lot, zoning restriction, access to lot, what under the ground, utility access, etc. If there is an existing building on the lot, condition of the building is important as well. I think you will need to contact an agent in your Newton to come in give you a free CMA. I said free because, many agent will do it for free, don't pay. Try to call a few of them so you can have different opinions.