Hello,
i think there are too many karts and tracks in SuperTuxKart 0.7. Indeed some tracks (such as amazonian track) are botched (ugly texture) and some karts (such as Tux Kart) are too old fashioned. So, I think you should reduce the number of official karts (15 to 8) and official tracks (20 to 10). You are a small team. You should concentrate your effort to a small number and use your addon feature. For some tracks you also should reduce their length. For the novice level, it's very long to finish it.
Another suggestion is to add a button "a quick try". At the beginning, a lot of people only want to play and doesn't care to play with beagles or tux. I think "a quick try" should have the feature: 3 opponents, 1 short lap, novice level and an explanation of the main key (<space>, V,B and N keys).
You also should to improve the sounds of supertuxkart. They are very poored. Consequently, people is quickly bored of supertuxkart.