No, I just talked to verizon and they said you will only loose your unlimited plan if you are a brand new customer or if you upgrade from a phone that did not have a data plan. So, since you have a droid 1 you wont loose the unlmited.
Not only do I work as a retailer for Verizon, but I just upgraded from 3g to my 4g Samsung Charge and I still have my unlimited data. And to answer the question that i'm sure is to follow this, yes i did it after the tiered data packages were introduced. So upgrading to 4g shouldn't impact your unlimited plan. It will only be taken off your account if you drop the package for longer than 30 days.