This affects more than just victimless crimes. The opponents argue that things like stealing a gun or snatching a purse would be made into misdemeanors when they should be felonies. I do have some reservations about this, but on balance it would provide some much needed sentencing reform so I'll go for Yes.
Guns are excluded according to the Prop 47 site. If you steal a gun or receive a stolen gun, you're charged with a felony. If you have a history of violent crime or gun theft/receipt, I think you're also excluded from misdemeanor treatment, but I wonder if every court will do due diligence with equal competence.
I agree with you on purse snatching and property theft. If someone steals a freshly cashed $900 paycheck from a lower-class person, it should be a felony conviction without question. The only way to protect the poor is to keep the felony property laws extremely low or to raise the misdemeanor penalties until they almost mimic a felony, without the felony stigma.