Let's say that I have 100 links from a PR8 website and I can get 1000 links from the same PR8 website. What difference will that make on my website? These are all legitimate links. Some links are of far better quality than other links.
Well, if all of those links of probably 3/4 of those 1000 links are of quality, it sure will make a bigger difference. But - if it is just for quantity and did not actually targeted a good or quality backlink effort then it is almost nothing.
Let's say you are trying to rank high for keywords similar to "stuffed toys". If you get 1000 links from PR8 domains, any of which has absolutely nothing to do with toys, it will most probably be less valuable than getting 100 links from PR6 or PR7 websites which are closely related to toys, and especially stuffed toys.
Honestly speaking only a few links from relevant pages would be of use. Sometimes you get backlinks from comments section/sidebar appearing in each page and these are of no use.