There's no rush. The plan changes with VZW won't happen until later this year (IMO it'll be right before the new iPhone comes out) and you'll have ample time to get something beforehand. Also note that you can keep your current unlimited data plan with a new phone, like the iPhone 5, if you pay the unsubsidized price. The iPhone 4S is currently $650 at full retail price.
I switched to an iPhone 4S from an OG Droid and haven't looked back (except that I really miss Google Maps). I don't know if I'd be comfortable going back to Android.
You'll be able to burn through data faster with 4G, but that doesn't necessarily mean you will. Also, it's possible that the 2GB thresehold will change with the new plans, maybe it'll be 3GB. I have zero inside knowledge on that.
From what I've read in publicly (again, no inside knowledge) the idea is to create a bucket of data (let's say 5GB) that a household would use monthly. I could then link two smartphones, my iPad, my PC, my car, or whatever "device" to that data plan. The bits would be shared. That's the idea anyways. It might not happen for awhile.
BTW, if you need to move now, check out the newest Droid Incredible coming out. It looks nice.
"Something in my vicinity is Carolina blue and this offends me." - HPR