There are "spirit houses" everywhere. There is one in the courtyard of my hotel, next to the hot water heater. (I love Thai plumbing practices except for the absence of traps!) I took this shot looking down from a station on the "Sky Train" (Bangkok's El).
They remind me of the "bathtub Madonnas" of Somerville, MA and other East Coast cities, but I'm not sure the visual and/or folk aspects really translate.
I see spirit houses as playful and positive, but perhaps they are not that, or not all that. After all, people make decisions based on dreams here, instead of rationally maximizing utility, or some such. Ghosts, as I understand it, are real. Perhaps others with more experience can comment here.