"Black box" stats in regards to NESing is an approach to play where players provide spending orders that go into a computational model to produce the end of turn results "automatically". Players do not have full knowledge of how the model works so they cannot calculate the effects of their spending ahead of time. Hence the "black box". Many NESes use a more "transparent" system where players can calculate the effects of spending pretty accurately: spend 2 EP and raise your economy 1 level etc.
I found that when I play in a game with very a "transparent" set of rules, I tend to spend my time planning and figuring out how to improve my stats to the specific levls that I think give me an advantage. I can usually map out several turns of spending in advance.
That is harder to do with a "black box" system. My hope is that with BirdNES players will focus on spending in character as if they were the king and get a sense of how things work over time. If you know the full effects of spending, you don't have to think about it, all you have to do is decide. If you don't know the full effects, then smart players do think about things before they act. They ask themselves questions. I would prefer that players think about their spending orders rather than just calculate results.