Sounds a very similar set up to ours, except that our KS1 building was built just after I left the school in the early 70's and the KS2 extension was tacked on partly in the late 90's and partly in the early noughties.
The smaller classrooms are a problem, but they don't tend to have as much stuff up on the walls or worse, pegged out on string hung across the room, so there's less visual noise, iyswim.
Insanity, I'd forgotten that - ds1 had a thing about lamp posts when he was little. He used to count them and knew where we were ie, almost at Grandma's house etc by which lamp post he could see. Mind you dh used to use counting the lamp posts as a means of remembering which bus stop to get off at when he'd been out boozing as a teenager - so maybe it's genetic. 
Another of ds's current minor obsessions is the built in sat nav in dh's new company car. Ds is obsessed with how often the length of journey time prediction changes. He doesn't like the fact that it might say we will arrive at X o'clock when he first checks, but then changes to a different prediction and time according to our speed and traffic etc. He no longer asks are we nearly there yet, but he constantly strains his neck to see if he can see the screen (cue getting clonked on the head by dd whose car seat is in the middle) and then asks "What time does it say we'll arrive now Mum?" 
He also gets upset if dh doesn't go the way the sat nav tells him to, so it has to recalculate the route - talk about back-seat driver!