For what reason? For the following reasons:
S - Being a maybe or a non-responder warrants being a "no" to me, and yet some others are not as steadfast. Being a maybe is self-focused, and can appear as though you were just waiting for a "better offer". Make a decision and stick with it. You are not doing anyone a favor by being at their party, so decide what is best for you, make no excuses or add any grandeur, and simply do what you say you are going to do.
V - It's formal etiquette, yes, and yet, it's just the right thing to do. Offer to participate before, and mean it. If that is not requested, then act on the clean up immediately on your own. Unless you are told differently, keep cleaning and enjoy the whole evening/event's experiences.
P - Arriving too early and going up to the door, or into the room, is just as unfortunate as being terribly late is. Shoot for a 15-30 minute range for arrivals if you are hosting, and have a call or something you can do out in your car if you are a guest. Plan to arrive within 10 minutes of the start if things are more formalized than a simple open house.
These RSVP tips are not mean to be confining or stuffy, rather encouraging and empowering. By RSVPing with kindness and care, thoughtfulness and follow-through, you will be a guest who just might have a ball, and get invited back!