Every wasted millisecond on the server side matters. It impacts scalability, customer experience (and revenue) etc. You should take every easy win you can get there.
Not doing full includes is just ridiculously lazy. It doesn't take that long to write them out, and your IDE can help you out there. I bet you spend more time on social media during office hours than you'd ever save from not having to type out those import statements.
Or the IDE. IntelliJ or ReSharper does that for me. And I like dealing with any naming conflicts right then and there, which those tools allow me to do.
I see that you've never worked on a project where the CPU time needed to handle the traffic with crappy code is much more expensive than developer time to write efficient software.
Burning cpu and maybe i/o looking for code all over the place is going to make it really hard to make it fast later.
Do you most of those need to happen at all, ever? In my mind, auto-loader is a sign that nobody knows what's being loaded (if they did, they would just require it). Requires should be full pathed (because have you seen what happens when you search the include path). Mysql_pconnect has been doing connection pooling for a long time, mysqli supports it too (so yes, you do need to connect sometimes), anyway, if you're loading a framwork, loading that probably takes longer than connecting to a mysql server in the same colo.