TBH its such a cool mod but its not easily removable if eventually the car sells, the ones I have seen come up for sale with the mod havent sold for loads more to come close to covering the cost. The eventuri is loud anyway compared to stock but being a coupe you dont get the same experience as the roady from a noise perspective. Also I think ive only seen one that actually copies the M3 CSL, the Z4 I dont think has enough room for the snorkel to the air ram so a lot of the ones ive seen arent attached to anything inside
So not sure if the benefit is quite like the CSL as that is vented to the bottom hole in the bumper for the air ram effect. Add the cams etc the increase is minimal and the cost it high. But it is super cool.
One of those, 3-4k is a big investment, if its a forever then ye deffo but in general I would say its a hard sell. There was a guy on Facebook that had the same dilemma but with a higher milage M roady worth like 10-11k wanting to do the same. I cant help but think that spending 30-40% of its value on one mod is not worth it and I cant see it adding loads of value to the car.
Most buyers like standard cars, although it's cool I would still rather spend that extra difference on a lower milage car. There will be buyers but it's even more niche in an already niche market.
For me the Eventuri/GruppM is is a really good compromise.
A good example is that Z4MR thats for sale on the forum at the moment with a few nice mods. 94k and 10k and no bites thats crazy. It is needing a front bumper respray, wheels refurbing and bearings/mounts your easily over 2k before you get going.
What ive found with mine, paid 14.5k for it already in 5k and it needs bearings mounts and a suspension refresh, ideally a bit of paint and the wheels refurbing too so probably 25k into it and its probably worth 12k.
Tough at the mo.