In an answer to a previous question of mine, one that asked about the planar orbits of inner planets, I was told the following (emphasis mine):
On the subject of different solar systems, I would expect tidal disturbances from close passes with neighboring stars to be the most dominant effect in determining how closely planets' orbital planes coincide. So... "urban" star areas would have more close passes than "rural" ones, and also more metal pollution. Ergo, if anything I would expect systems with higher metals to be less coplanar.
Now, this last sentence got me thinking whether or not there was any evidence for this, so do stars of higher metallicity have more planets in highly-inclined Pluto-like orbits? (higher metallicity means more dust, I'd presume - but would it significantly increase the gas to dust ratio?) I actually would expect the opposite hypothesis (at first), since there might presumably be more friction with more dust (and the amount of dust wouldn't really affect the amount of gas, since gas still forms the overwhelming majority of particles)