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That being said, it is hard to say if you should. I advertise our brand names there because, especially with OV and adwords, the ads appear in places that don't have SE results, only the ad results. If your ad is there, you will come up no matter what.
But, there is a large amount of places that your ad does appear next to SE results, so if you are already on the top SERP, it may be redundant. Or not, because it still may be profitable to be there.
The best advice would be to test. Figure out your ROI, with the branding value of appearing where there are no SE results included and see if it would be best for you.