hosting promotion materials on another domain ?

[samebb]

I don't know much about SEO but I've been told that affiliate linking does not boost SE rankings. If that is infact true, then I don't see an advantage to your proposed scenario.

Thats very true, but there are many ways to combat that issue. Using cookies this can be solved, but aside from that issue, the links themselves wouldnt be such an issue.

The SEO advantage would be in optimised pages, and the sheer volume of traffic and links to the domain.

for instance if you have 10 sites, affiliates are linking to 10 domains (sometimes),

If you have 10 sites and affiliates are all linking to the same domain, with internal and external links, it would provide a lot of advantages SEO wise.