Quite so. A job which requires a pilot to use his A&P needs to be paid extra to compensate for the additional duties. Otherwise, the operator is abusing your higher qualification and you're working for nothing.

Depending on how busy you are in either capacity, you'll need to watch out for duty, rest, and fatigue issues. While a corporate pilot does not have a FAA-imposed duty and rest limit, the bottom line is that he or she must still operate safely, and the same is true of a mechanic. Don't let yourself be put in the position of compromising safety margins, and don't allow your skills and certifications to be abused with underpay.