Well the fact is we still don't know anything for sure yet. It's starting to look like you may be able to keep the unlimited package if you upgrade after 7/7, IF you have a smartphone on your plan already. We certainly don't know that, however, and there's no telling what will be included and what won't be (Blackberry's, older Palms, WiMo, etc). We also don't know whether you will be able to upgrade from a 3g smartphone to a 4g phone and keep unlimited, there's no difference now and we don't know if things will remain that way or not.
All we know for sure is that if you do not have a smartphone before 7/7, unlimited data will NOT be an option when you upgrade. Feature phones with the Vpak or whatever are NOT considered smartphones, and unlimited feature phone plan are NOT compatible with smartphones. I had a $15 a month unlimited VCast Vpak, and you can't run any smartphone on that package even if you buy it outright.
So if you want unlimited data and don't yet have a smartphone, which was the case for me before the Charge, you had better pick up something now. And it makes the most sense to get a 4g phone now, as again we don't know if you'll be able to upgrade from 3g unlimited to 4g unlimited after D-Day (assuming this is even true that they'll let you upgrade with 2 year pricing and keep your unlimited).
As far as activating a smartphone on your account and switching to a smartphone data plan without signing a contract, there's no telling. There's technically nothing stopping them from forcing you to switch to tiered data after the date even if you keep that OG Droid, since you never signed a contract. I'm sure they wouldn't do that, but I definitely wouldn't count on them allowing you the opportunity to upgrade without losing unlimited if you had never signed a contract on a smartphone with them in the first place. Then again, they say the data packages aren't actually part of the contract, though you are required to keep one for 2 years if they sell you a smartphone with 2 year pricing. So its your call on that one, no reason to waste an upgrade if you still love your Droid and aren't too excited by the available LTE phones. But if you want to make sure you're locked in to unlimited LTE, there's really only one choice.