Upgrades to the Z4 E30: Where Do You Draw the Line?

As we all know, the Z4 E30 is a fantastic car, but let's be real, it can always get better. I'm curious to hear your thoughts on what upgrades are worth considering and where do you draw the line between performance enhancements and potentially sacrificing the car's original charm. Are there any essential mods that are just a no-brainer?