I thought that the feet on my ZyXEL P660 router seemed too small to allow cooling air to flow easily underneath, so I put four small wooden blocks under the router. I also set a monthly reminder to brush the dust from the vents (we have four dogs, so accumulate more dust in a week than most households see in a year; how many people do you know have to dust the vacuum cleaner before using it? :-) ).
The upshot is that the router always feels cool to the touch. I don't know if this helped anything, as I've forgotten what problem I was working on when I first did this.