MarkT:
I think you need WAYmore gain and a proper instrumentation amp (very very good CMRR). The change in resistance of a strain-gauge is measured in tiny fractions of a percent, so gains of 1000 or more aren't unreasonable.This might be useful:
http://cerulean.dk/words/?page_id=42 there a gain-resistor of 10 ohms is used, meaning a gain of 6000. Sounds more likely than 50!
I agree, still I was hoping to see some small change at least with a gain of 470, but it might be the amp as well, I'm thinking of trying one of the INA amps preferably with an easy gain adjust