This is such an excellent idea - I've spent the last few hours reading through the whole post !!!
In addition to many of the sites you've all mentioned, I've found a really cool site that helps you plan a trip to anywhere in the United States (so far), based on the attractions that you can find in any particular region. So, if I go on vacation with my family, and one likes skiing, one likes shopping, and the kids want theme parks, I can find all of those things that are within driving distance from each other. Then I can also find hotels in that resion too.
The site is www.tripcart.com, and if you look for whatever type of attraction or thing to do in their "search", it will open up a google map with lots of icons for the things you want to look for. You just click on an icon (or a few) and it all shows up on the map, then you go to one that looks interesting, click on it, and it gives you the option to look for "nearby attractions", "nearby hotels" and the like. As you go along, you can save all the things you want to see and do in a personal trip.
Happy planning