Next thing you know, you'll be asking why anyone on a bike cares about how fast they're going - if they wanted to get there faster, they'd just take the car, right? :-P

If you're using your bike for transportation, speed always matters. It's just that you don't care about extra seconds, like racers do, instead you care about minutes. I would definitley buy newer, more expensive tires if it meant that I got to work 5 minutes faster!