I have a coupe of sites that I don't really know what to do with. They are both quite old but I am bored with them as they don't make any money. Both are PR4 (naturally, without spamming) what would happen if I redirected them to other unrelated sites that I am still interested in? The links would not be all that relevant to the sites that I am redirecting to, so would it do harm, good, or nothing at all? Would google see it as spam or is this a legitimate use? If that's a bad idea, has anyone got any ideas what I should do with these 2 strong but otherwise useless domains? Thanks!
Are you talking about redirecting them or just adding a link on them to a website that you are interested in. I believe that the best case scenario in both cases is that nothing happens. Since they are completely unrelated and there is no actual website linking and it it simply a domain then there can be no value added.
I was talking about 301 redirecting the whole of the domain that I'm not interested in to the one that I am
Relevance has become more and more important these days. I doubt you would gain much from redirecting irrelevant sites to your main site(s). Maybe you could contact some people with sites related to the sites you don't want any more and see if they'd like to take control of them...maybe sell it to them. You could also look into ways to try to monetize the sites, perhaps through Adwords or something.
You may sell the website as a PR4(organically achieved) is of good value and can be used by SEO firms for back linking websites in same niche. Also being PR4 you can add something to your website to get traffic, being PR4 it's easy to achieve good serp for relevant and medium competitive keywords. Redirection to non related domain does not give good results.
Don't redirect them to unrelated sites. Either re-build them into useful domains or let them expire and save some $.