FTDNA will only retest the 5 unique markers in the Y-37 test, DYS570, DYS576, DYS607 and CDY (2 copies). The will drop the 11 unique Ancestry markers.

The main reason to upgrade is to get your sample stored for next generation testing. You can designate someone to control it in case you cannot give another one. The full Y-genome tests (Big Y at FTDNA) will be much more definitive and the price should decline rapidly. Who knows what else is down the road.