DON'T LISTEN TO YOUR LISTING AGENT!!! If your corner of the world is about to be developed, then your listing agent is probably seeing your property as a easy turnover. He knows that there will soon be high demand for your property, which means selling it would require no effort on his part. He wants to make a quick and easy sale and pocket his commission, even if selling right now isn't in your best interests.
If you really want to know what the property is worth given its development potential, you'll need to hire an appraiser. A good one. Try to find one who holds the MAI designation (the highest designation a commercial appraiser can attain), and don't settle for anything less than a specialized commercial appraiser. Estimating the value of land with development potential is not trivial. It's not cheap, either, but it's money well spent if it prevents you from selling your property for fifty or a hundred grand less than it's potentially worth.
Development land is worth a lot more than its square footage and existing improvements would merit. Exactly how much more is a question for that highly qualified appraiser. It might be 10% more more valuable, or 50%, or maybe even 200% more valuable. Or there might be some factor that prevents it from having any increased value. It all depends.
I'd try to estimate just how much the development adds to your property's value (again we come back to that appraiser), and then compare that against how strongly and how quickly I want to move away. But above all, don't do anything without being properly informed. Don't do anything rash. You might have an opportunity at a windfall, so don't piss it away.