We are in the same boat @Fozzle.
GMG has a sale on all the DLC, so I did some research and it seems that these are the best in terms of quality and content:
Snowfall (we own this)
AfterDark (we own this)
Natural Disasters I am on the fence with this one, the reviews on Steam mention it causes a lot of forest fires for the player to combat, in addition to other disasters. So this could turn every game into California Wildfire Fighting Simulator. Not sure if that something I want.
Parklife looks fun, but its pretty new and I am waiting for 50% off or more sale.
IMHO all the dlc for this game is double what it probably should cost, hence the wait for sales. :)
The remaining music and cosmetic dlc are probably not worth it, I don’t feel they add anything that is MUST HAVE.