Welcome Moss.
Don't get too hung up on MPG.
25mpg will cost you 40 gallons per 1000miles
40 mpg will cost 25 gallons.
So the difference is 15 gallons.
Therefore even at 5000miles p.a. the difference is 'only' 75 gallons - OK at £5 per gallon that's £375, but on a car with minimal depreciation, and low insurance costs, it's hardly mind blowing.
Having said that, beware of road tax banding. Some Roadsters fall into the £400+ bracket, and that can be avoided - earlier ones and later ones are slightly less.
Check dealer websites to see how depreciation hits - most have a new +4 in stock and the MMC website has loads of used cars for sale at present.
It's a balance of 'Your Spec' against somebody elses used car.
I've no regrets about going used. If you buy right you'll be depreciation free.
