You don't need the relativizer that in either sentence, or the verb in the first or the auxiliary was in the second. Why clutter your sentences up with superfluities?

We helped ourselves to the snacks on the table.
We helped ourselves to the snacks laid out on the table.

So the only question is whether you want to put any emphasis on the fact that somebody laid the snacks out for you.

Consider: "Detective Flanagan listened carefully and then proceeded to the kitchen. An untouched roast chicken lay on the table, with carving implements at the ready. Detective Flanagan stepped closer to examine the two wine glasses at the place settings. One of them contained some dregs of wine, and a smear of lipstick on the rim."

The chicken had been lying there for a while, but I bet snacks would see a lot of action pretty quickly! This would work: "I slept until 10 the next morning. When I went to the kitchen to make myself a cup of coffee, a colossal mess greeted me. Several empty snack packages lay on the table, and a trail of busy ants was working on collecting crumbs of potato chips from the floor under an upturned chair."

Is there any reason to prefer one over the other when dealing with inanimate objects? Is the choice between these two possible sentences simply a matter of style/emphasis on position vs. placement?

Sorry I didn't answer this explicitly. I thought my position was clear from the context. Basically, I think you've put your finger on it with "position vs. placement." Lay on the table describes a state of being. Laid out does too, but with acknowledgment of a discreet action in the distant past.