To me you need a new case which won't cost a lot.
Example Tecware Nexus Air ATX around $70.
Newer case the airflow is more direct since it is not block by the CD/DVD + HDD rack which
are mostly old design.
So air will be push in more with modern case not to mention hardware like GPU are getting
hotter and hotter.
Or you can just change all the case fan to Artic F12 which cost $12 each.
But I think the front of the case is choke up, maybe you got time you have to wash
the front.
Let it dry first before putting it back.