I agree that amazon suggestions are not great, but Amazon have a fairly limited set of information to go by - only your previous purchase and search history on that site. If Amazon had the same amount of information that Google/Facebook has, they would be able to make much better recommendations.
As an aside, Amazon should really have an 'I already bought this somewhere else' button. 6 months after searching on Amazon for a watch but then buying it elsewhere, I'm still getting watch suggestions...
I know for music they have a button like that. I go through my recommended albums every so often looking for new deals and they have two buttons: 'I already own this' and 'Not interested', which means those items get hidden and it updates its recommendations.
It's actually pretty neat and I think its definitely made the recommendations more useful. I think it can be done for videos as well, but I guess they don't have it for general retail.
As an aside, Amazon should really have an 'I already bought this somewhere else' button. 6 months after searching on Amazon for a watch but then buying it elsewhere, I'm still getting watch suggestions...