I think there is a TON of room for improvement for what amounts to AJAX requests for notifications and chat messages.

CodeSatori is on the right track with what he found. Something to think about, XML parsing can use a lot or resources. For the type of data that is being returned are all of these includes, functions, templates, and parsers really needed?

What if there was a very simple 'pending notices' table and instead of issuing multiple requests for different information across may tables see more requiring lots of steps every few seconds, the client simply asked 'is there anything waiting for me?'. The notice table could even contain a 'pay load' field so there is no need to do an additional request if there is something waiting.

I see the issues as two fold, updating the server side to this new table and updating the client so you only have one thing polling the server (kind of like Apples push notifications) that can check for notifications, then trigger the required client side feature.