Single Comment

The advantage of any exchange can be simply expressed by the strength(or
value) of the pieces being exchanged.  If a game was populated with pieces
of near equal value, the advantage of exchange might not be significant. 
But if the pieces were of various degrees of value, enough to clearly
differentiate them, exchanges would hold the potential of an advantage.

Yes, a player can make sacrifices to obtain positional or material
advantage.   This gambit would not be possible unless there was a prior
consideration of the value of such an exchange.  But whether or not the
exchange is a gambit need not be part of the determination of a game's
potential for advantage in exchanges.