Inversions are actually pretty meaningless on the guitar. Everything is bunched together, and there are repeated notes all over the place.

Take, for example, a D chord in first position -

2
3
2
0
0
x

You've got two A notes repeated, two D notes repeated, and an F# all by his lonesome. This doesn't adhere to any of the definitions of an inversion or a triad. It's just a jumble of notes.

So in short, with the guitar, knowing inversions isn't that critical. For piano it is, but not the guitar.