ok i see the point and i understand your will to improve on what you have, well if you have those 500 usd. extra why not then, you will get disc brakes and 9 speeds and better components, by all means install a rear rack and panniers (panniers go in and out very easily, they are bags to carry your stuff) inside the panniers you need to carry, at all times, a U-LOCK (it is a super lock, difficult to violate) and replacement tubs and tire levers, and a HEX wrench, the rest of the space in the panniers is where you carry your laptop, or whatever you need for work, you need a red flashing light that goes in and out your pants or your rear rack, or your seatpost, and a helmet, mudguards or fender would be optional, depends on the climate on your area and your willingness to bike in the rain,