I would have to see a plat map of your property in relation to the lot being developed.
I would also need a road map with the most travelled throughfares marked as well as the DOT impact study summary.
Then I would have to visit the site and see what it looks like now and visit other sites of similar nature to yours and see how they look with a comm. dev. in front of them.
Then I would need to pull up sales info and historical assessment info on simliar plots that have a simliar development situation like yours.
After that I would give you a range of possibilities for value influences based on the best information I have and then bill you thousands of dollars for my professional study.
The town that I live in is already considered prime real estate. It has some of the most expensive homes in the region. (mine is not one of them, unfortunately). It also has the best schools in the area.
Edit: I like the idea of having them pay me the difference in property values. That way, even if I sell the house for less, I won't take much of a hit.
In my experience this development isn't going to cause any drastic decrease in property values. "Property values" are also a very subjective thing based on their highest and best use to the intended user. So you can't really get concrete information like "That development will definitely make your property decrease in perceived value to the tune of $50,000". Few residential appraisers/assessors would ever give you a pinpointed number of possible value change, there is too much liability in that. Commercial guys might be more inclined, but they will also state that there is in no way a guarantee that any of their conclusions are correct.
Don't even begin to entertain ideas of having the developer "pay the differential in property values". That's just not going to happen, ever. The only true point in that line of logic is that they could possibly buy you out at some point in time. Though from my experience you're property isn't going to be considered viable land for purchase in this developers eyes. If you were even a faint idea then the planners would have contacted you a long time ago.
Here are the influences I see from my experience in the profession. You've stated that your area holds some of the most sought after property in the area. The values of the houses don't always have an effect on property values until the area is above 75% developed, so take that out of mind. The commercial development of your area is a near sure-fire sign of positive development and increased desireabililty of your area. Commerical development usually directly follows residential development, and in some rarer cases, leads it. At a macro level all signs point to increased values in your area, which includes your land.
Now on a micro level there could be different stories. The micro level is harder to pinpoint due to the different driving forces in the typical homebuyer. Some people may find your property less desireable due to the destructed view of the back of a commercial development. Some people will find your site more desireable due to it's newly found central location to all this new development and potential for future development. Some many not care about any of the perceived external influences due to their strong desire to own your specific house. I could go on for a while about the various influences in the eyes of the typical purchaser.
In the end it will most likely be a positive result for the area and you. The area is, if you're truthful about current values, experiencing rapid growth and expanding its civil/commerical infastructure to accomodate heavy residential development. You shouldn't have much to worry about, except mabey over-crowding in the future.
You can take your fight to the developers, city counsel, DOT, county planning board, whoever you like and they will listen to what you have to say. It may not influence them in their plans at all, but in the past a large public uprising has caused commerical developers to look elsewhere. Though keep in mind that fighting development, in a value/business sense, is foolish and couter-productive.