That smell idea is pretty cool actually, better than using the standard a* path finding - which isn't quite how zombies work.
I think only zombies that are already aware of a player should be able to lock onto the smell path though, or at the most it should increase a zombies awareness if they stumble upon it.

This has inspired me to revisit my zombie swarm simulator.

Depending on how 'dumb' you want your zombies to appear (actually pretty cool illusion when i tried something similar a while back), crash and turn actually does work pretty well.

Just avoid anything concave in your environment that they can get 'caught in'.
Or simplify any concave geometry to use a convex collision hull (even a bounding box/sphere looks fine).

From overhead it should look like one of those old 'ball-drop' games where you drop balls in at the top and they slowly bounce down through the pegs until they reach the cups with points at the bottom. Nothing should get trapped though, provided the world isnt concave, and they should eventually reach the player. And dont worry , although i said 'bounce down' they wont actually look stupid and bounce lol.

Even if you do have some concave things, you could do a simple timer for each zombie that ticks up when the zombie remains in a small area for a longer time than you would expect. That would identify which zombies are probably 'trapped' and allow you to act appropriately.

The great thing about zombies is that you can dumb down the AI because it actually IMPROVES the player experience as the zombies do things which match a player's expectations.