It depends on your expected ROI. If you spend the equivalent of $20 to build and maintain for a year, but get $40 out of it then that's not a bad return. If you can find 100 or 1000 niches like that, all making that return, you're set.
It won't take you much to optimize for that keyword so you might as well if it promises to be converting well for you. For example: "Buy spanish books online" might only have 11 searches per day but if that's what I'm selling...sure..there's chances that the keyword will convert well.
No u should keep it continue but still u should use tha keyword like mesothelioma, adsense, yahoo hostings, travel etc.....