Is the BMW M3 CSL a good investment?

The thesis

The E46 M3 CSL is the ultimate naturally aspirated inline-six BMW: 3.2L S54 with 360PS, 110kg lighter than the standard M3, and a 6-speed manual. Only 1,383 built globally, with ~422 for the UK (RHD). Prices have climbed from £40K (2015) to £80–140K today, with the best examples exceeding £150K. The CSL is the last truly lightweight, analogue M car before turbocharging and weight gain. However, the appreciation curve has already run hard; this is a 'hold' not a 'buy for maximum upside' play, and sits at the top end of budget.