When it comes to professions and apprentices, that is a local phenomenon anyway. No adverse effect on path finding. To the contrary, that lightens the load. As only non local citizens require heavy path finding, e.g. armies, bandits, traveling birds in autumn, though those are a bad example as they fly ;-). All commoners can use cached computations. They go to work and stay there for a while, then some celebration and shopping. A lot of talking and maybe flirting and admiring, but that's it. Only few can afford holidays and travels frequently, researchers more maybe?
Armies bound to only occasionally updated "roads" mostly for logistics reasons. Local short term path finding at frontiers at operational level is another story. That is where the trees play a role. But that is more static than in 0AD where the only thing to see often is brutal killing, no friction, strategic warfare. And it requires micro there where your generals handle it here.
Formations progressed, that helps. Only group leaders require path finding.
Here officer system helps: War isn't every unit (group) finding a way always. Adversary armies most often hold lines. That's why soldiers' life is boring and senseless digging and constructing, moving predefined paths - until this sudden moment, death not far. These operational units are the only having path finding switched on. (that includes mushroom gatherers, so it depends on the action performed, as it is event driven, that toggle is computational not expensive)
Oh they abducted your quarter general? Speculate about her knowledge getting extracted, exposing your weaknesses. It may be time to sign that peace treaty or barricade all paths to your small peaceful realm. General mobilization is another option. The choice is yours.