As the saying goes, "How fast to you want to go? How much do you want to spend?" If you like the W140 and can afford to keep one going, by all means do so. I personally don't care for that platform for a variety of reasons, but that shouldn't keep you away from one if that's what you really want.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.