In the UK what you're looking at isn't too bad for a 19 year old car! We sometimes have salt on the roads in the winter and that's the main cause of the rust. UK mechanics aren't frightened of rusty bolts, it's a standard problem. Things were much worse back in the 1980s when I first started working on cars. We had hard winters and there was much more salt in use. Suspension bolts had to be undone with the application of heat to break the rust bond and get the thread moving. Brutal - compared with the methods you're suggesting - but very effective!

 

Use anti-seize compound on the threads if you live in an area where salt is applied to the roads in winter. It slows the corrosion and allows the bolts to move easily.

The X200 is prone to rot in the sills, so it appears this one is still okay if it passed MoT. You may want to spray the underside of the car with a light oil prior to the onset of winter to protect the suspension components.

The rear subframe should be cleaned or sand blasted to remove the rust then sprayed with a rust inhibiting primer before being painted. This is also a good time to replace the bushes, which are usually worn.