To take the two extremes: Is everything you do meticulously pre-planned, analyzed, and executed in the exact same manner every time? Or do you 'let your feelings guide you' to spontaneously do whatever you feel to express while playing, giving potentially an entirely different performance each time?
I'm sure most people do a some of both, but to what extent? Personally, I think the ideal is more of the latter, which has to do with my favoring of 'method acting', and the pursuit of 'emotional truth' in my performances, even to the extent of deviating from the score if you feel the need. Or do you think that is mostly over-idealized hokum when it comes to classical piano?
I wouldn't say I "pre-plan" or "analyze" everything, but I surely do study how to play it so I don't get up there and drum through a piece.
I study the feeling in the piece, study the dynamics, and then add changes that I feel are appropriate to the piece, and let the music guide me. I would never go up on a stage and perform what my feelings "spontaneously" led me to, because most likely that would mean I'd rush the piece, and ruin it. I think you should have a true understanding of the music when you have reached the stage, so as not to "spontaneously" play, and possibly ruin the piece for everyone in the room, not to mention your performance.
Now, if you were to perform it and feel something was missing, by all means, fix it for your next performance!
If you're talking about the hand flinging, head shaking and foot stomping so many of the classical performers do today, no. I find it utterly ridiculous. Your movement during a highly emotional piece should not make you writhe like a worm or appear as if you were dancing an Irish jig on the bench. It should flow with the music.
If you're REALLY feeling the music, then your body will move appropriately, and there is no reason to pre-plan. Just like people who don't feel the music sit straight like a board and play stiffly don't have to pre-plan to do that.