I will flush out my thoughts here on the subject. First, some definitions. An exploitive strategy is a strategy against a specific fixed strategy. For example, villain always bets $100 on the river as a bluff, so you call with all bluff catchers (the latter is the exploitive strategy, the former is an exploitable strategy). What we're familiar with is finding the maximally exploitive strategy (MES) (i.e. choosing the strategy to maximize EV against a particular strategy).

Optimal strategy is then derived from the idea of MES. We are hero, and suppose villain plays the MES against us. In other words, he adapts his strategy to maximize EV against our strategy. Hero's optimal strategy is the strategy with the highest EV against villain's MES. Equivalently, the optimal strategy makes villain indifferent between their various exploitive strategies (I'll leave it as an exercise. It is fairly simple to verify using the definition of optimal). This second definition (the exercise) is most useful in actually finding solutions to particular game theory problems.

There is an important property of optimal solutions worth stating. In practice, optimal strategies tend to be mixed. Mixed meaning that you choose action A X%, action B Y% instead of always choosing A or B. The key property is that the EV from any choice from a mixed strategy is the SAME. Say we're on the river and are deciding whether to bluff. If villain was exploitable we'd either bluff 100% or bluff 0%. If we don't know villain's tendencies we choose an optimal solution (against his MES). Something like bluff 30%. The key is that our EV is the same whether or not we bluff.

Thus, in the game theoretic approach to poker there is no value in choosing inferior strategies (i.e. -EV type plays for 'image'). Choosing inferior plays for future EV is a purely exploitive approach! Put more bluntly, game theory advocates believe that metagame is irrelevant.

I hope all that is correct. More to come.