One other comment I'd throw out which is tweaked from advice I give to people looking for a camera and asking what the $4000 camera gives them that the $1500 camera doesn't.

As a general rule I reckon if you don't know what the extra money buys you, or you don't know why you might need what the extra money buys you, then you don't need it. So if you're in that kind of situation get the cheaper option and enjoy it. When/if it breaks you'll hopefully have learned something about what you want, you'll have given yourself chance to find out more about how you want to use it and so on, so your next purchase can be made with more information.

If you buy a $500 mountain bike and by the time you've worn it out you realise how much you love the trails then you know it's worth spending $1500 on a better mountain bike. If by then you realise you like to go offroad but won't ever put it through anything demanding you might decide to spend $1500 on a hybrid/touring/cyclocross bike. If you realise that you only ever ride on tarmac and want speed you might spend $1500 on a road bike. It's just a shame when people spend $1500 on their first bike only to realise within a couple of months that it doesn't do what they wanted.

My LBS gets a customer every once in a while who drops four figures on a road bike and then complains that such an expensive bike doesn't work on rutted gravel tracks - in their mind an expensive bike should be able to do anything. Personally I'd really struggle not to suggest to such a customer that they try taking a Lamborghini round a rally circuit.