I think that given that this is a hobby project, then some level of over-design isn't really a problem. You're doing this for the enjoyment of creating something, and you don't have a deadline.

So some level of over-design isn't really a major issue - who knows, maybe it'll turn out to be a very valuable part of the program.

In a commercial enviroment, you really have to balance the design, weighing initial programming time against ease of future additions / maintenance. The CS books say more attention should be given to the future changes, but in reality, people don't care about tomorrow, they care about now. And besides, it's never easy trying to predict the future.