It's all risk based really. You're the risk that your existing car will continue to have things go wrong with it (though some of the items are just routine servicing matters). But if you buy another second hand car with a few years behind it and tens of thousands of miles on the clock, there's the risk that will need repairing too, on top of the monthly payments to buy it.
Clutch, cambelt and brakes are basic service/maintenance issues really - they'd be expected to be replaced as they're mileage based, and certainly the brakes and cambelt should have been replaced as per service/schedule. Was nothing highlighted when you had it serviced previously? The garage should have been checking against service schedule what needed doing and when.
A "new" car at 60-70k miles will also probably need a cambelt change (if not done already in previous services), likewise brakes do wear out over time, so again, depending on whether it has been serviced properly, may have been done recently or may not. You can get a "feel" of the clutch during the test drive - sometimes it may already be slipping or be very "light" at biting point. Best to check the service history per the service schedule book and MOT history online to see what's been done and when. MOT history usually shows up previous failures and advisories so you can see what's been done and what hasn't!
Personally, I'd never buy a used car with over 50k miles, and not one with over 10k per year on average. You just don't know how well/badly it's been driven, and things like clutches, gearboxes, suspension are all highly dependent on previous driver care. You can, of course, be lucky and get a well driven, properly serviced higher mileage car, but again it's a risk!