I did the sums buying mine.
£8250 66 reg 9 miles.
Road tax £20/yr
Insurance (currently) £240/yr
Miles 8000/yr @ £0.11/mile £880/yr
Service (first two yrs) £200 appx
Service and MOT after two £250 appx
So not including tyres and other stuff, if there's no major breakdown/failure for the next 7 years it's £1400/yr.
Thinking a taxi return to town is £8, I could have 175 return taxi trips for that!!
Your costs (upfront and insurance) is far below average, and mileage below average - however even if they weren't and your road tax was £140/year, your cost per year would go from £1400 (plus tyres etc) to £1520 (plus tyres, petrol, etc) -- less than a 10% rise.
You're using 735 litres of petrol a year. Petrol is currently £1.20/litre. In March 2016 it was £1.03/litre, in 2013 it was £1.40. A return to pre-brexit prices would save you £122, an increase to 2013 prices would increase your cost by over £200. Sure buying the car in March rather than April is worthwhile, but the extra VED cost is insignificant compared with petrol fluctuations alone, let alone when factoring in the other costs.
VED changes have very limited effect on a rational buyer of a new car.