That's a decent bike, keep riding it. If it ends up being too fragile, find a 90's mountain bike, get some double walled rims and ride it with no worries.
Upgrading a bicycle won't make you faster, really. The mid-low range parts are just as, if not more durable than the high end stuff, and cost a fraction as much. Riding position is what makes the largest difference, way more than a few pounds ever will (unless you ride up mountains all day.)