"So to get to the point, would a Masters Degree in Aerospace Engineering benefit me at all, in addition to a CPL(H) IR? What are the employment alternatives/advantages of possessing both qualifications, if there are any at all?"
Looking at the question from a different perspective, there are no disadvantages related to possessing both qualifications. If you have the time, money and intelligence to pursue a Master Degree, you should. Employment alternatives are greater for those with a Masters Degree in "anything" compared to those without. It is a key that will open a door that you may one day wish to pass through.