Lame_Wolf - 10:35 pm on May 13, 2012 (gmt 0)

However, more adverts do = more opportunities for one of them to catch the attention of (and be of interest to) that particular visitor.

Then place them well.

More adverts means more chances of off-topic adverts.
More adverts means less competition for the slots allowed.
Less adverts means more competition for the slots allowed.

Ad blindness is ad blindness, no matter how many you have.

Do whatever you wish, it's your site.