This does rather highlight how one man's meat is another man's poison. I wouldn't want to be seen dead in it, but that doesn't mean it's wrong. Personalising objects can be an expression of independence or a form of 'rebellion' depending how it's done; after market stuff on cars appeals to many who want that little bit of individuality, I suppose.
But in my humble opinion, having an XM (or BX or CX or whatever) is enough of a 'statement' to make in itself. I love the lines and design of the XM. A nice series 1 would be highest of the lot in terms of 'purity' of design, but I love my S2 - and I believe it's probably an easier car to live with. If it's a good example I see no reason to put additional stripes, spats, tail pipes, alloys, badges
(I must tell you the XM I acquired recently had metallic foil stick-on Maserati badges on it - and a Xantia's V6 badge on the back FFS! - now thankfully removed - what was the guy thinking?!) etc. on the car. It just makes it look naff and cheapens the look. Sometimes I think it would be forgivable if it contributed to the capabilities of the car - (a subtle bonnet scoop on a BX TZD Turbo for instance - giving better intercooling), or wider alloys for bigger discs and chunkier calipers maybe - but is the original so in need of modification?
Under the bonnet is a slightly different matter as a lightly modified and tuned engine in a 'standard-looking' car can be a pleasing thing - but mainly for the occasional 'Q' car surpises.
As I said. My opinion. I suggest the lines are pretty well drawn between the 'purists' and the 'personalisers'...

1995 Citroen ZX 1.9D Avantage 3 door, white 106k miles.