Ever have someone say this to you?  The fact is if we didn't keep reinventing the wheel we wouldn't be where we are today.  Can you imagine driving a car with wooden wheels?  Progress requires reinvention as well as new inventions.

I understand the saying really means don't recreate the exact same thing that already exist, but most of the time people are just trying to make something better or cheaper not recreate the same thing that already exist.  Then there are some cases where someone doesn't know that the same thing exists and believe they are just creating something anew.  Is there anything wrong with either of these cases?  

Creation and recreation is always valuable and should be encouraged, if nothing else you gain experience or come up with a different way to do something; it only becomes an issue if it wastes time and money (someone else's).  But if you believe in something and can do it without costing someone else time and money then go for it.

Today with the internet we can quickly research and investigate what is already invented and quickly evaluate if your need can be filled with an existing product or if you need to (re)invent it.

So I say by all means reinvent the wheel and keep reinventing it.