thedogscar, I was exactly like you in that I had a THunderbolt and when it died a friend gave me his THunderbolt. unlimited 4G is just amazing. I easily use 10G per month and once used 50G when my wifi at home wasn't working for awhile.
I paid full retail for the Icon and would advise just buying a n LTE compatible phone to use with your account. VZW will not suddenly abrogate your contract; it is yours unless you change the plan.
personally, I love not having to ever worry about using too much data. the overage rates are crazy.
you don't necessarily have to get an Icon; I picked up a 928 on ebay for $80 and it worked great.