Yep, an event firing doesn't actually do anything or consume any system resources. That only happens if some addon (or some part of the default UI) is listening for that particular event, and runs some code in response to it. Like Semlar said, if you're seeing framerate drops when an event like ACTION_SLOT_CHANGED fires, one of your addons is doing something very wrong. All the events you listed are just very frequently-firing events that don't really mean anything most of the time; most addons should not even be listening for them, and if they are, they should be doing only minimal processing in response to them.
You can
install a CPU monitoring addon to see which addons are
actually consuming excessive CPU time, or if you can reliably reproduce the FPS degradation,
use a binary search pattern to quickly narrow down which addons are causing or contributing to the problem.
Once you've identified problem addons, update them if possible, or just disable them if there are no updates; if they've been updated recently (eg. since WoD release) post a comment or bug ticket to let the author know about the problem, since someone with a more powerful computer will be able to handle addons consuming more CPU time without noticably affecting FPS, or there may be other factors (for example, if the problem only exists when both Addon X and Addon Z are enabled, but not when only one or the other is enabled).