Flight sim - yes. £1200 computer - no!
I have an old version of MS Flight Sim and an even older computer. I used it to practice flying the routes for the IR and I still use it before getting back in the Sim. It mainly helps on your scanning, but can also help in understanding what the needles are doing.
If you can, get a copy of RANT (Radio Nav Aid Trainer I think) as well as a flight sim.
£1200 - thats 2-3 hours in a twin or about 15% of your total IR - spend it on that instead.