One of the biggest factors that affect computer speed is the fan.
If there are so many dusts on the fan, laptop will get hot easily and will not perform well.
Based on my experience every time I clean the fan, my laptops worked like new.
Problem is it's too hard to remove all components.
So I wish there was a seperate cover over the fan that I can remove and clean the fan easily.
Status Update: Please see bill_b's comment for further information. Thank you for posting.