Is 80 hex required just for synchronization or does it 
have to be sent with each bootstrap loader command?

The 80 hex is sent as a synchronization character before each 
transmission. The device responds with a 90 hex as an acknowledge. 
Then a data frame is sent. Each frame begins with a header byte = 
80 hex. The other bytes of the frame follow the 80 hex header 
immediately. The correct format of the BSL data frames are defined 
in the application note `Features of the MSP430 Bootstrap Loader`
SLAA089 available in the MSP430 website. 
A careful examination of the code included with the application 
note `Application of Bootstrap Loader in MSP430 w/Flash - Hardware 
and Software Proposal` SLAA096 shows that this is the proper 
technique. The software and hardware in that application note have 
been tested and proven to work.