I get what you're saying, I just still need some sort of picture / video to highlight this for me!
I have zero problem getting mansions and expensive housing I just don't seem to be able to sort density out. It's driving me mad and it's holding back my population.
I can't find one.
Just get a bus depot, and buses stops up. Get a school up and school bus stops.
Also police/medical/fire helps a lot.
Then watch click on the house and watch. If you got a green arrow, then just give it time. However before it upgrades density you need appropriate road around them. The bar is split into three and the road comes in three levels. So you match to the next stage. Or just upgrade in one go.