Stick to the interval. It might cost you three or four hundred quid (plus water pump, which is usually cheap). If your belt breaks it will almost certainly wipe out your engine. Dunno whether any cars come with "safe engines" these days. Many moons ago I had a Vauxhall Nova whose engine survived a busted belt. Great little car it was. Eventually the driver's seat sort of disintegrated. The main problem was the colour, best described as faecal brown. At least I got it cheap off a mate. £800 and it lasted me for years. Never let me down. Luckily, that belt busted in Bude.