Learning by increments is an approach that you might like.
Just play the game with whatever moves you feel are best. After the game, go over it with an MCO or a computer openings database and see where you or your opponent deviated from the main lines.
Stop right at that point! It might be move #4 or move #10. Either you or your opponent did something out of book. You guys are evidently not GMs so there's less a chance of a novelty and a greater chance of a mistake during said deviation.
Merely learn the "one move" that is considered best according to theory at that point. Most good books on openings will tell you why a certain move makes more sense than the others, or why certain moves are just plain bad.
Ask a strong player why that move makes sense if you are not convinced.
So there, you've grown your repertoire tree by one more "leaf".
Rinse and repeat! (Yes, this takes time, but it is the easiest way for person to actually learn (not memorize) an opening, IMHO)
I usually keep notes of my "opening play book" and just like the above, I incrementally add to it weekly by playing as many slow games as I can. One additional fun thing I've noticed is that some openings seem to "fit" better than others ... in certain systems I seem to be playing book moves purely by following general principles and during my post-mortem, I realized that I deviated from book 5-10 moves later than I thought I did. So it may not be as slow and arduous as you might think it is.
I have recently just started playing chess again after several years away from the game. Even when I was playing before, I was never much more than a woodpusher. This time I am trying to actually study a bit, but I am boggled at the range of opening theory that is out there. I have tried to learn opeings (in fact, i am kind of fascinated by opeing theory) but find that even when I attempt to choose lines of play that lead to narrower numbers of "good" responses I still end up looking at a huge number of lines.
Does anyone have any practial advice for a casual player who is trying to move beyond the basics in terms of openings? I find that the great majority of the time I am just winging it, trying to play by basic principles like control the center, develope rapidly, move the king to safety, etc, but I feel at a significant disadvantage. For example, if I open e4 and someone throws a sicilian at me, I fell like I am either playing into a system my opponent knows better, or making dubious moves just to get "out of the book".
Maybe I am just being neurotic, but how does a lower level player get a grip on the opening phases of the game?