Steve, here is what I do to bring Sue around to my way of thinking.
I utilise a subtle blend of psychology and extreme stupidity.
When I wanted to buy the first Impreza, I spent weeks talking about buying a Nissan Skyline R33 GTR until she was fed up of hearing about them.
The Impreza then seemed like a 'sensible' alternative.
Just start looking at something like a cheap Maserati or other similar monumental money pit (pretty much anything Italian)
If you manage to make a convincing job of the deception, the S-Type R will look like a rational purchase !
Or
If you like a bit of danger and excitement in a relationship, casually walk in one afternoon and whilst discussing your day at work, drop in 'oh, by the way, I bought another car today'
Better than the New Years Eve fireworks !
Or so the crash team told me when I came round in A and E.