I'm fairly certain that they wander without being disturbed by anyone.  I've had a map where the wildlands were isolated by my faction, so no one could get in without going through my cities.  I didn't go in.  They still came out and started wrecking cities, one by one, until they were all gone.  I quit the game before season 50 because I'd lost 3 cities.  I can't stop those armies at that level.  

It's not just discouraging for new players.  It's like "Roll a die to see if you lose."  At least with the +1 city sight you'll get an extra turn and maybe you can prepare, but if what you're preparing for will easily wipe out your entire military, there's not much point.

Will they be less likely to attack weaker cities or less likely to attack stronger cities?  

Wandering monsters from lairs don't bother me even if they get close to my cities, but monsters shouldn't leave wildlands undefended, those two obsidian golems guarding the entrance to imperium always wander off letting any low level character grab their high level loot when they aren't home. [.80]

Well, I guess this is a step in the right direction. This definitely helps in reference to monsters wandering from wild lands. In my opinion, there is a still a core issue with the player having to deal with the AI's irresponsible settling behaviour. This was demonstrated to me once again just recently as I was happily playing Capitar and (ironically) killing another Capitar faction. I take two of their cities, including one that had engulfed a lair (umm, I forget now, the big Skath one). For dozens of turns the bloated dragon wannabe blissfully ignored the AI until I conquered the city. I made the choice to go after the city because I didn't care if it got razed since, despite claims on the board to the contrary, I knew that the monster would get its hate on as soon as I showed up. And so it came to pass. Except this particular Skath marched not to the newly taken city, but through 3 stacks of unlucky spearmen and into on my own well established cities, burning it to the ground. 

Please. at this point, just put in an option for the monsters to ignore the AI players. I will gladly concede this boon because it goes so frustrating to have AI mistakes ruin a game I am enjoying.