I would refer you to the yahoo/realestate/values web site. This may not be the exact address but I did a simple Google search and this turned up.
Basicaly this site can help to tell you what your house is worth now. You can use that information to determine what you should or should not do.
I have always been told that you do not want to over improve for you neighborhood. So, of course, that is exactly what I did with my first house. I was going to live there forever so, why not?
I installed a full dormer on the rear of my 26' X 34' Cape, I then had to add a 28' wide X 30' deep garage with the second floor tied into the house to match.
I paid 60K for the house and added another 60K (by the time I was done). I ended up selling the house (I was never going to sell), for 149K and it took forever to sell it.
My neighbor sold his house the next year for 110K and had done no work on the house he paid 70K for in a snap!
Yes, my house was much larger and more modern. But, no one wanted to spend the money for that neighborhood. Besides, the 29K above what I had put into it minus the real estate fees, did not leave a good taste in my mouth when my neighbor landed 40K, less the fees!
Learn from my mistakes, check out the real estate values!