Yes it does. Rewriting existing code is an excellent way to learn. Just don't use it in production until it's been thoroughly tested and you're sure of its quality.

Most people's objections to reinventing the wheel are that 1. your code will suck 2. you won't be creating anything new and useful and 3. they're just regurgitating a common misconception because they want to feel smart. As for one, see the above paragraph. As for 2, you have to learn before you can contribute. So definately go for it.