In my opinion, one of the 'Golden Rules' of Internet marketing has to be the following:

'Once you have uploaded a website, you should leave it online forever - even if it is only making you a couple of dollars a month.'

As long as you are covering the hosting and domain registration fees each year (maximum of a couple of dollars a month), then why take the site offline? Admittedly if the site is causing you hours of work every week and still only making you a couple of dollars income each month, then yes, remove it. But if the site involves you in no work (for example if it sells an eBook or you generate Adsense income etc from it, then why remove it?)

The point is that whilst the site in question may only be generating a small amount today, you never know what might happen tomorrow