Q: Must one always discard the Object when using it’s power?

A: If it does not say you have to discard it to use the power, then no. Rock, Paper, and Scissors remain in play when you use their power. Money, on the other hand says you have to discard it from play in order to use its power. The MacGuffin and Backup MacGuffin’s power depends on the presence of other cards on the table or in your ownership, but if you’re able to use them, their power is to remain in play, essentially.