Alright, here's my predicament. I would like to start commuting to work most of the time. I am just getting back into cycling however. I have an old Specialized Hardrock that's been in storage and could use a tune up. It is kind of ugly though and part of me wants a nice shiny new bike. I think I would be ok if I just got the tune up and threw some slicks on the Hardrock, but the gleam of a new ride still intices me. My budget would be about $500. There is also a charity bike ride this summer I would like to participate in. If I were to buy a new(er) bike, what is best for commuting? A road bike? I really have started to like the idea of a road bike, but don't know if that would be the best setup for commuting. Oh, my ride would be a bout 6 miles each way, with one major hill (uphill on the way home). A good portion of it is on a busy road with construction. I have no option but to go through it. However, it is a fairly rural road that they have built a nice sidewalk that no one uses. I am thinking about riding on that until the road conditions are better. If a cop stops me, I'll point out the safety hazard of being in the street

So my main question is, if you were me would you fix the bike you have, or get something new(er)? if so, what would you pick with a $500 limit?