You really need to evaluate the driving conditions you're going to see. An all-season tire is adequate for all seasons, but it's not really good at any of them. While we tote things like handling at the limit, since we're dealing with a "sporty" car, there's also other factors like braking that come into play for people who don't need the "at the limit" handling traction. The tire is the only part of the vehicle that is in contact with the pavement, so you want the best traction possible at all times. A 2' difference in stopping from 60MPH can be the difference between automotive buttsex and a buttpuckering close call.
If you're dealing with sub-40° temperatures regularly, that's where the winter tire compounds shine; they're designed to give ultimate traction in colder temperatures. If you're not dealing with a lot of snow, you can look at a set of Performance Winter tires, which are designed mainly for dry traction, but will also offer superior traction on snow/ice superior to an all-season tire. Then you have your summer tires which also provide superior traction to an all-season tire. If you really don't see that much sub-40° temperatures (above 50°, the winter tire compound gets a bit greasy and doesn't grip as well), a set of A/S tires to offset your summer tires during the "winter" months is ideal.
While having two sets of wheels/tires is a bit of an initial financial offset, it's evened out by doubling the life of the tire (since it's only being used half the year). There's also the issue of storage; not everyone has the space to store an extra set of wheels/tires.