I've done computer tech work, and I suppose I'm just an all around geek for most things IT related.. But yes, dust is horrible for computers! It can essentially build up a layer on your mobo and other components which acts as insulation trapping in heat!
Thank you indeed for the reminder to everyone :D Currently I'm crunching on a laptop which could probably be checked for dust soon. Otherwise I'm running an Apache web server off a Raspberry Pi 3 in my bedroom hooked up to my TV.. I'm actually almost curious enough to let it get dusty for a short period of time to take before and after specs as well...
Edit.
Also don't forget to replace cpu and gpu paste before it dries out over time and extreme use, or have a tech do it if you're not confident.