If the car isn't costing you, apart from fuel, insurance and tax, isn't due a timing belt, or something else expensive - then I'd be tempted to keep it.
I'm running a 2001 Audi A4 2.5 TDI quattro avant. It's done 150k, and is in good condition. Still get 45mpg on steady runs (without trailer). I service it myself and got the local garage to replace the timing belt last year. It just passed another MOT in September, and I looked at the possibility of replacing it. Found a new (2010) A4 Allroad for sale, but at £21k it's quite a jump, so my wife knocked the idea of replacing it for at least another year. My budget will be half of what I was originally looking at!
Ideally I still want a 4x4 (harsh winters where I live) plus temperatures as low as -18 a couple of years ago.
On my list so far... (will need to haul 750kg unbraked trailer)
2010 Volvo V50 1.6 Drive SE Lux with start-stop, £30 or less road tax, up to 75mpg. I know its 2 wheel drive, but very fuel efficient and most comfortable leather seats I've ever tried.
2010 Skoda Octavia 4x4 or Skoda Yeti.
What's on you list?