Here’s a perspective you don’t what to hear:
My top three mods: none, none, and none!
I was a long time car guy. I even ran an automotive machine shop for years. Back then I could do anything I wanted to do to a car. We could build custom exhaust systems (we even had a car lift - no laying on the ground to work), We could resurface heads or engine blocks, overbore or sleeve engines, build up crank shafts and the grind them back to original size, etc. Any tool I needed was right there in the shop. Plus I got parts at cost, and sometimes less: I was given a Ford 427 sideoiler block by a customer who didn’t want it anymore. Needless to say I took advantage of the company’s generosity and spent a lot of evenings working on my own stuff.
Looking back it seems every car I modified always end up with more problems or another mod “that just had to be done”. I also seen it with other people who modded their cars. After a while I got tired of the endless stream of mods and fixes. Not mention the money I was out.
Reliability is the best feature of any car in my “old man” opinion.
So now when I look for another car, if I see any mods, I’m done looking at it. Modded cars do not sell for more.
My 2003 zed is all factory, the previous owner always had it serviced at the dealer and today it is performing perfectly, I hop in and go. That’s all some people want. Here in the USA I see Z4 prices going up pretty quickly, I could turn a nice profit on mine after owning just under a year with zero money invested into mods.
This is just my view point.
BTW, I don’t think rebuilding the VANOS or a new DISA a mod, those kind of thing are maintenance.