Writing an interpreter (or compiler) greatly enhances one's programming skills.
It's important to re-do things which others have already worked out, in order to reach a greater understanding :)
I learned how to implement Lisp by reading the source code for multiple compilers. Started with Franz Lisp, then KCL and CMUCL. I don't feel that a toy interpreter is going to teach the same things.
A toy language won't teach the exact same things, but it covers a lot of the same topics.