Is there a benefit to a pilot/aviator having an FCC GROL license?
There's no tangible benefit to having a GROL in getting a pilots license of any kind as getting the license generally confers the right to use aircraft radios. In some places you need to get an RT license for aviation as a separate test, however that's pretty minimal. A GROL is only good for repairing, maintaining, and running certain types of radio stations. 

An A&amp;P will let you work on airplanes, but it also does not help get a license. An A&amp;P will give you insights into how an airplane works, but you can get those insights without an A&amp;P. Having an A&amp;P and a pilots license might be a different story if you plan to work in remote locations where being able to fix your aircraft when it breaks is useful. It won't help you get a flying job in most places.