If your current bike is still in relatively good condition, I would personally keep it, perhaps upgrade a few components but probably not. A new shiny and expensive bike will not make you a better biker, unless you are into competitive cycling and high-tech components give you that split-second edge over the rest of the pack. Instead of spending hundreds if not thousands of dollars for a new bike, I would do a complete DIY tune-up or have it done by your LBS, and invest in proper commuting accessories like paniers or baskets, lights, fenders, better tires, etc. I moved back to Yellowknife a few months ago after being away from there for 5 years, and got myself a used Trek MTB for $100, equipped it with used fenders and a front basket that I got for free at my community bike shop, got myself rechargeable USB lights and proper winter apparel, and I've been using it for my commute and to run errands in temperature as low as -45 which is the norm at this time of the year.