On my weekend projects, the thinking is usually "What's the most fun I can have building something?" and then I go build it. We don't need to apply deep level strategy to everything, sometimes it's enough to just build fun things. If it ends up being useful, damn, what a great weekend. Either way, your skills and experience by Sunday have grown relative to Friday. Any benefit derived by others is just a bonus.
OP, keep on jammin' on the weekends doing whatever makes you happiest. :D
I started off with a kinda boring job, mediocre graphics skills and the tiniest grasp of C syntax. Now I get paid to design and build iPhone apps. It's awesome. But it all started with little side projects to sharpen me up. Start practicing, you can do it if you commit.