As Tinsnips said, you don't really want to get a car that is basically the same, and a whole lot of dosh more expensive. Even going from an sv6 to new SS. If you're maybe planning to play a little with the current one, it isn't unreasonable to suggest you could hold onto the car a little longer than you'd planned. Look after it well, and km's, up to a certain point, are irrelevant.
I had a similar issue when I was thinking about selling my VT Calais. I had always been a big fan of the VZ range, but really wanted something that held no similarities to my VT. So I started looking at the VE. So, my advice would also be that if you really can't hold onto your current car for an extended period of time, at least wait for the VF to launch.
Above all though, a house should be a priority. A house is an asset that generally gets more valuable with age, whereas a car depreciates at a rate of knots. Financially, it's a no brainer.
