I thinks it's better to offer surfers a wider choice. I'd rather come back to a site that offers a bigger number of links for me to surf around, than one that only links to just a few sites.

Also if you offer less links, your content (and those few links) need to catch the surfers attention or he's gone. If a surfer hits your site and there isn't something he likes, chances are that he might find something interesting in your blogroll. So I'd say that having a variety here is a plus.

From my experiences there are always a couple of sites that sell very well and of course it might have it's advantages to just promote them. But why not grabbing the odd sale from other site as well, expecially if it doesn't cost you anything extra. If it only results in a payment every year or so, it's still money I wouldn't pass on.

I think there are better ways to push the good selling sites than just dropping the underperforming.