Another Renaultsport Megane owner here. I've got a 2015 Renaultsport Megane 275 Nav (with Cup suspension pack + LSD). I've owned the car since Feb 2017 when it had ~5700 miles on it (recently ticked over 26000 miles). I left the car pretty much standard for 2 years apart from throwing a Ramair foam panel filter in it. The car had to have the gearbox and driveshaft replaced under warranty last year as a driveshaft failed and damaged the gearbox. Got that sorted under the 4 year Renault warranty and from what I've read it would have cost me upwards of £2000! The warranty runs out this coming September so hopefully I'll be trouble free for the rest of my ownership
Recently I've had the centre silencer removed from the exhaust and replaced with straight pipe. The car sounds a lot better for it, lots of rumbles and coughs/pops firing out of the back. No annoying exhaust drone either which is a massive bonus! I'm averaging ~27MPG in my car with my daily usage. Sitting on motorways at 70MPH ~35MPG is easily achievable so it's not too bad.
I've previously owned a tastefully modified Megane 225 and a Clio 172. I still miss them both for different reasons. Can see me keeping my 275 for another few years yet though, definitely the best of the 3 cars! As you can tell, I like my Renaultsports!