Yeah, whaling wasn't that common among the colonies during the early 18th. I think the earliest record of a whale being caught in New England was off Nantucket or Cape Cod around 1713...or is it 1703? Something like that. Whales were caught during the 18th, but it wasn't big business until later in the century and into the 19th. It was bigger in Europe though...so maybe their paths did cross!
At any rate you're right, it would be a damn valuable haul. I could be wrong, but I think the primary source of ambergris was to merely find deposits of it washed ashore. I know Dampier talks at length about that. I'll have to dig out his books so I can find the specific chapter, but he talks about exploring Ambergris Cay or some island off Belize and finding some mammoth chunk of it that would pay for the whole voyage. Apparently he tried in vain to convince his crew of the value, and finally talked a few of them into helping him lug this monster piece on board, but I don't know what became of it.
Time for me to do some diggin! :)