I'm not sure if I'd have the b@ll$ to buy the XM - the suspension system is enough to give me sleepless nights...
Regarding the choice between the Vel Satis vs the Avantime - I guess it really comes down to whether you plan on carrying rear-seat passengers. The Avantime has often been referred to as a reverse tardis (there is less space inside than the exterior would have you believe), whereas the VS is an extremely spacious car for up to 5. The other benefits are; you get the option of a diesel (I have the 3.0DCi, which has loads of torque, and at least 35mpg no matter what), plus, since is is still in production (in a lhd format), parts supply should
be less of an issue.
I've had my car now for 18 months, and added just over 30,000 miles to it - the only unforeseen expense (touch wood) so far has been a new battery due to an electrical short.
Its a real pity that Renault stopped selling this car in the UK, as I would have another one without hesitation.
I would suggest that whichever you purchase, that you investigate aftermarket warranties (cost & coverage), as these cars aren't mainstream models, parts are priced accordingly.