as you say, worst case, the disc will be unbalanced and the unit will make a lovely screaming noise.it'll be fine to use just to see what's on the discs and copy them off if required.
but as Patio states, if the info isn't important, why even bother, apart from pure human curiosity of course.
not to sure about soaking them in water however.
depending on the type, the majority of discs for ages have used an organic dye between the substrate material and I don't know how they would like water getting in.i've seen quite a few discs with a 'rot' infection, presumably from moisture.