I spent most of the last 3 years bashing around doing survey work in a C150 Aerobat. Not twin work, obviously, so a little different for you I'm sure. Absolute hoot and some of the best flying I think I'll ever have. £20 per tacho hour, so it'll never make you a wealthy man (unless you buy out the company - some serious money to be made there), but you will enjoy it.
Just don't be had for a fool - remember it's your licence on the line - and keep the peepers open for low, fast pointy things. I guarantee they can ruin your whole day.
Well worth the experience, as it keeps the hours trickling into the old logbook, and depending on the type of survey and hence the flying required, it'll sharpen those handling skills to a high degree. For my money, much more rewarding than instructing.