>if its only function is to send you to some affiliate offer - it's spam //

I don't think this definition is quite right.

A site can be good and still have as its raison d'etre referring you to a product manufacturer. After all any sales website is doing the same thing, there's just a certain distance between affiliate sites and the manufacturer.

Don't get me wrong, a lot of affiliate sites are bogus, unhelpful and given unwarranted prevalence in SERPs; but that doesn't make them all bad. For example in the UK there are sites that offer money back on all purchases - they're affiliate sites that share the affiliate fee with the purchaser.