I am now interested to find out what these 'problems' are you speak of, cos I am struggling to think of any.
The ONLY one I can think of with mine is changing headlight bulbs as it has perspex covers over them. To fully weatherseal them I have put a bead of clear silicone around the edges of the stainless covers. That would need breaking and a new bead installing afterwards. I reckon about an hours work in total.
Bear in mind, I'm only thinking about my car as an example...
Most of my switches are home-made modules that replicate the BMW switch, but they would have to be re-sourced from suppliers who may not be there when the time comes.
One is common to many of these cars, and it sounds like the sort of thing Lady Bracknell would say. It's obviously not going to hit you in the face.
ANY modifications to the monocoque could mean the vehicle needs an IVA. It would take a VERY thorough inspection to confirm none have been made.
You have used spinners that are not just cosmetic. What tests have been done to confirm they are safe to use. In Germany, for instance, parts fitted need to conform to the relevant DIN standard. Taking the car to Germany may (I emphasise "may") cause problems. Taking it to Italy will definitely cause problems, unless all the "F" badges are removed. Even then, it is for you to prove that it doesn't infringe copyright. At the moment, these laws are domestic - they may become EU wide.
Servicing - I notice that you have a smaller bonnet. Does that cause any access issues, or does the front clam shell need to be removed to do any job that would be easily accessible with the Z3 bonnet raised? My bonnet raises, but not as high as a Z3, and it doesn't have a service position.
Tracking - as I mentioned in your thread, you may need to compensate for the different wheel arch height if it is different to the Z3 height. As a new owner, I would need to know this.
Accident damage - where would I obtain replacement panels if required? Tribute isn't going to be there for ever, and I imagine that when Chris goes, so do his moulds.
Glass - same problem, maybe.
Plexy glass headlight covers - same problem, maybe.
All fixtures and fittings were supplied from various sources without spares support in the contract, so if anything breaks, it may be a case of having to buy two, so they match on both sides of the car.
Paint matching - my car was originally painted Ferrari Rosso Rubino 308, and I was also supplied with a 250ml tin. The tin was scanned, and the best match was a Hyundai colour. The car was scanned, and it's best match is to a Peugeot colour. One extra drop of any of the paint colours used making the paint can change the colour. When cars are painted at the factory several cars (say six) are painted at the same time, so one drop may become 1/6th of a drop error in the paint colour.
As I said, I'm happy to live with these problems on my car, but the exam question was "Would you want to own this car?". My answer is "No"