Always with Bach's contrapuntal music, there's a horizontal aspect and a vertical aspect. Sometimes one comes to the fore, sometimes the other. Even in a piece with 2 or more distinct voices, they're not always both equally interesting. Sometimes one is just providing harmonic support for the others.
So yes, there will be times when one of the voices (not always the top one) takes the lead, other times when it's more interesting to play them as equals. It's very hard to generalize, and even in the same piece, good players can handle it differently.
As for staccato/legato -- neither one is going to make your piano sound like a harpsichord! So don't even try for that. I'm finding with the Goldbergs, for example, that there are places where the 8th notes need to be legato, or half-staccato, or full staccato. There are certainly ways to do it without indulging in romantic excess. (Sixteenth notes I generally play legato, but I'm not dogmatic about it.)
I think Bach very consciously tried to make his music as abstractly beautiful as possible -- some of his pieces may never even have been intended to be played. That's why transcriptions of his music for almost any instrument still work. Including transcriptions for the piano...