I would get new valve cover kit. It comes with new gasket already installed, bolts in place. Just old one off and new one on. Dont have to scrub old gasket from valvecover and install new one on there.
I have heard that some shops dont replace gaskets anymore. They only do the job replacing the cover aswell, because the same customer comes back later with cracked valve cover. Valve covers i havent heard of warping, but they do crack and leak oil. its common.
So if you are going to remove wiring harness, uninstall fuel rail and coils to get to the cover, then i think its better to replace the cover aswell. You get new PCV valve with new cover too. That can cause problems on N54 engines aswell and they are built into the valve cover.
Prices: Oem valve cover kit is around 400 USD. There are aftermarket ones as cheap as 200 dollars. Better aftermarket ones that i would trust like VAICO are tiny bit cheaper than OEM, around 360 or something. So i would go OEM to be sure. Gaskets are 10 times cheaper.
So your choice: Save 350 bucks and risk doing the work again later, or do it all at once and be done with it.
If you want to DIY. There are excellent guide videos on youtube how to do it... they are mainly 335i but its all pretty much the same. Its even easier in the Z, more room and no cowl you have to remove.
https://youtu.be/bJGvN9HNJuw
I havent replaced mine yet, But i do regularly check my valve cover because i know its coming soon and i want to catch it before there are pools of oil in the engine bay. Thats why i did some research on the matter.