The best Opening strategy
The opening repertoire is a choice of a player. It reflects the player's style and preferences. What is better - following the theory moves or improvising on the chessboard? I think, there is no clear answer to that. I know the players that do not know the opening theory yet playing extremely well. For them the main burden of play lies in middle game. It doesn't matter that they do not get any advantage in the beginning - they understand the position and can easily win by gradually improving it or getting into tactics.
These players usually play something like 1.b3 1. b4 or 1.f4 (or 1.e4 b6 for Black), in other words unpopular and less studied openings where their positional and/or tactical talent shows better.
The beauty is that one cannot easily refute those openings, and it requires quite an effort to understand how to turn them to your advantage. This approach is good in a way that makes other players think right from the beginning. You make them get away from their regular schemes that they study so thoroughly. With an experienced player this trick won't really work.
Personally, I think that knowing the opening theory is rather advantageous. For me the opening theory resembles existing guidelines all deviations from which are signals to think. In general, if there is a certain opening variation - then the position had occurred in a significant game and was an object of study. Deviating from main lines usually doesn't make your position better but often makes it worse (unless we are talking about a significant improvement of the variation). Here lies a vague line between a good and a bad move. It is especially notable in sharp openings like King's Gambit, King's Indian, Sicilian etc. where you need to know the variations move to move in order not to lose right away.
It is almost certain that every regular calm position has several possible equal moves. Which one of them the player chooses - depends on the taste, the vision and evaluation of the position. If the player wants to win - he must search for the best move in every position. That's how we gradually accumulate the advantage. If the player is more cautious - any of the equal moves is actually ok.
True that the variations are developing all the time. The unknown variations become popular, the popular ones sometimes get refuted and put in archives. The openings are subject to fashion as well. I bet that the Trompowsky is going to be way more popular now because Carlsen played so. Sicilian Najdorf was popular as Fischer played that way etc.
What is your choice? Do you prefer the unknown or a theoretical dispute in a popular variation?