How to keep improving and break through a plateau.

I have been using PHP professionally for 3 or 4 years now. I have done a zend engineering cert used a few frameworks and am about to start a new job using symfony.

I am pretty good at noticing language ‘wtfs’ and using the documentation from frameworks and tools to get things done. Personally I’m interested in app architecture/design, scaling and performance.

I feel like I’m plateauing however. How do I find out what I need to do to take my skills to another level. What kind of projects will help me. It’s hard because I don’t really know what to improve at as I have been working alone for the last year and a half.

Also are there any projects that you can dive into more advanced stuff without setting up loads of CRUD if you’ll excuse the pun! My last couple of projects have just felt like work rather than learning and pushing myself.