A capacitor, in parallel with the motor by itself, will actually make the problem worse since it significantly increases the turn-on current surge, which is usually what welds the contacts. An RC snubber reduces arcing when the relay opens and that could help protect the contacts from that. So the answer is no to a parallel capacitor and yes to the RC snubber. The resistor power is generally negligible since the there is significant current through it only when the contacts open.