I, too, was a paper boy and lived by the tips and Christmas money because I treated my customers like royality. Every paper was always in the door or a protected spot determined by the customer. I haven't taken a paper for nearly fifteen years because they just drop it at the curb.
I value great service and tip very well when the service merits...and I am calmly constructive with people when the service isn't what I expect. I rarely decline to tip regardless of the service, but always hand it to the person and point out the specific reasons for the small tip. I always try to hand all tips to the people and comment on the service.
For the valets try the tip if you think you should....worst that can happen is they give it back.