I would advise you to pass them on, it can make your business look suspicious when you hold that many domains, especially if you don't have any direct relation with them.
Its also quite annoying for people who might have, when they find that some blood-sucking parasite, stole them from under their nose.
You could however offer these domains as a "limited-time" offer, in other words, offer people a free domain if they chose your hosting solutions, that would also be likely to indirectly optimize your page further, in the moment people hear about it, and start linking to your business, from their potentially higher-PageRank sites.
Links from those domains are going to do nothing for your PR and there is no point in using them unless you partcularly want to build a link farm. But link farming is an overhead and if you are not prepared to do it properly, get rid of them. They are a distraction and you will get more mileage from an outdated list of free directories.
Back links are back links. They will work. And you will be able to "manage" the anchor text you want. But it will be expensive to maintain and there is a good chance that Google will pick this up as cross linking and penalise you. There are far easier and more cost effective ways of getting 280 back links.