Is the BMW M3 a good investment?

The thesis

The E46 M3 (non-CSL) with the 338bhp S54 straight-six and manual transmission is the last naturally-aspirated M3 and sits at a critical juncture. Standard cars trade £18k-£30k, materially below the CSL (£60k-£100k+) but have begun their climb. Low-mileage, unmodified examples are becoming scarce as the 25-year rule brings E46 into 'certified classic' territory. The S54 is rightly revered; the manual is essential. However, prices have risen steadily since 2015 and the market has begun to separate excellent from average examples. This is mid-cycle, not early, but a clean car under £30k still offers upside as the CSL halo effect trickles down.