As a CakePHP core developer, I think it makes sense to move if the following are all true:

  - You run a primarily blog-like application
  - You do not need a lot of custom coding - other than template features
  - You are comfortable rewriting everything to use the WP structure
  - You know the limitations of wordpress and they do not affect you

If only some of them are true, just add the features you need to your blogging platform.

For the record, there are plenty of plugins that allow you to 301 redirect old links to new urls.