Not much point upgrading a bike with a cheap frame. The frame is a critical component of the bicycle ride and handling. The problem is a new bike with a good frame is expensive. Second hand bikes are much better value if you're willing to learn how to modify and maintain them.

It's easy to get obsessed by these details and forget the joy of cycling. I was riding in Amsterdam recently and looking around at the bikes these ardent cyclists are using every day is surprising. Very basic machines, many looked fifteen years old, at least. No one wears helmets or spandex pants. They just go about their business swiftly and silently on a vast network of dedicated paths. It was cycle heaven.