Why dont you keep the VX? firstly of all it ticks most of the boxes, you havent owned the car that long.
Surely there is ample room in the back for your kids, large boot room for projects, its not the most practical car in terms of MPG, petrol and parts such as tires are expensive, as you went for the VXR! - but as you have already stated you can afford this, in your situation with hindsight I would stick with what you have. I trust that you bought the car outright.
I think if you sell it, your going to miss all the toys and spec of the car, I think you`ll be making a mistake.
Either this or settle for something like the mondeo, maybe a lower spec so you can afford a newer model, doesnt seem right to me to trade in a 1 year old top spec insigia for a 5-6 year old car. You could easily get a 2-3 year old focus for £6-7K, there cheap to run and insure.
I did something simailair to you becuase Id thought it would be cheaper to run in the long term, also I needed a diesa - l circumstances do change. When I look back now I kinda wish id kept the Astra, my astra was newer than the diesal I went to, plus I got stung for a few repairs on the car I bought.
With regards to your original post, why dont you stagger your projects, if you paid 20K outright for this car you cant be that bad off, it sounds a bit extreme to sell the car, to unlock cash to do projects.