I have known several folks that have re-shingled their roof with good results. As in, patch the bad section of their roof and not redo the entire roof. If there is not any significant impact damage (say from a tree limb), you should be able to inspect your roof, see if the asphalt paper has torn, decide on whether its ok and just re-shingle or install some new asphalt paper and re-shingle. My den was re-shingled in 2003 and it's still been working pretty great.
Good luck!