I've shot with both on the same set- not exactly an a/b but definitely shooting the same sorts of shots. I thought the 150 held up really well next to the 170. 170 wins the edge for image quality but dang close. I'd at least suggest a rental of a 150 to see if the image quality works for your application. I think it's an amazing value for what you get and the SDHC cards are cheap as dirt.
The HMC150 is not switchable at all. The HPX170 can be upgraded for US customers with Authorized cameras in the US to be switchable. This can be done follwoing their registration for the Extended warranty.
Jan Crittenden Livingston
Product Manager, HPX500, HVX200, DVX100
Panasonic Broadcast & TV Systems