There are two ways to improve one's life: improving the quality of each day and increasing the number of quality days. Cycling helps both of these areas.
Cycling improves the quality of each day by increasing the enjoyment of that day. No cyclist would argue with that! Just the increased stamina and feeling of well being, not to mention fewer sick days, is enough to do it for me (and of course, time spent on the bike.)
Cycling increases the quantity of days (on average) a person will live. Some have suggested that for every hour spent exercising,
a person may add an hour to their life (sort of the reverse of that old cigarette smoking statistic.) If that's true, the time spent cycling might actually be "free time." In any event, no one can argue that cycling doesn't lengthen life. Not only that, but it lengthens the number of healthy years a person has, so that they remain relatively energetic and healthy right up to the end.
Cycling is not the only thing in life, but I believe it helps one get the most out of it.