Welcome to WebmasterWorld Guest from 188.8.131.52
But it's unlikely that your visitors are seeing the same ads over and over. Unless you have a lot of unusually dedicated regular visitors, most visitors will only see one or two pages of your site.
You could always experiment, but I have found that blocking only a few advertisers can have a surprisingly large effect on my earnings so I would advise you to proceed with caution.
Would it be a good idea to filter some of these 'overused' ads, in hopes that Google will display a new AD, and maybe even a better paying one?
I wouldn't. I don't filter my competitors because some of them pay very nicely and it doesn't bother me if they make money as long as I'm making my money too. My sites are just affiliate sites with adsense thrown in but I'm in a pretty competitive market and if you start whacking out the people paying for these ads you'll be reducing your earning power by degree.
Then there would be a downturn in epc and I'd get nervous and clear the list.
In the end it is better to leave the list empty - survival of the most productive. The only advertiser I exclude now is my domain name.
And, if you can, add another paragraph with some word stemming/synonyms and you may get a few more advertisers in the mix. The more competition the better for you.