One man's spagetti code is another's masterpiece!
If it's working for you, no need to re-write. If you need to expand and your current development team can't understand how to scale up the old system, you will need to re-write.
Having people code the "right" way is tough. I have difficulty with this almost every day. I'm sure it will be tough for you because you won't know what you are looking at.
I suggest not only looking at frameworks, look at development methodologies. Agile and Test Driven Development (TDD) are currently hot topics and I believe good ways to go.