Regarding this short conversation between Jesse and myself, I've started to think that the default behaviour of Amount.p.toString() should be to return the numeric string with no unit/currency markers, so that e.g. new Decimal(amount) would work without any special Amount-detection code.

The with-marker behaviour could be implemented optionally, e.g. with .toString({ style: 'long' }) where style: 'numeric' would be the default.