I need ideas for my 18,000 simcash.

I have been playing this game for over 3 years now and never spent a single penny.

All I ever wanted to do was to collect as many coins and simcash as possible.

I collected over 15 million coins which I spent on sakura roads and now I'm left with 8.1 million only.

I have over 18,000 simcash on me and I am thinking of buying train cards ( as suggested by a fellow subredditor )

I don't care about designs. I need max population hence I don't have to purchase fancy good looking shops/entertainment/parks.

Any suggestion would be of big help.