OR you could take the view that when it goes in for the timing belt to be done, you could ask your home-mechanic to have a listen about and go from there. If it's a keep-forever car, the extra £450 or so might be well worth the investment. Me? I've done the belt as that really is dicing with death and they do fail. I'm not doing the chain though: my car just isn't worth it as a speculative bit of maintenance. If the chain should happen to fail, by all accounts although it's a right regal pain to rectify, it's not 'that' much worse than doing the job in the first place.
More to the point, the number of actual failures is tiny. Would be an interesting poll actually.
Anyway, as I've said before on here, there is a grave danger of writing a car off just via an expensive wish list. If it was a gorgeous £4000 example, it's a no-brainer: get it done. If it's a £1000 cheap daily, and you're contemplating an additional 45% of its value on something that will probably not fail (and even if it does, isn't like a cambelt failure), well that a whole different kettle of goats. Much depends on how much you like it, value it and how long you're intending on keeping it.
Anyway, I've had three TDi 75's: 175K miles, 155K miles and 205k miles. None have had chains, none have made any chain noises and so far at least, no failures. If they did, I'd cross that bridge then. I just listen now and then and take a close look at the oil when it gets changed. I have, however, done full cambelt kits (with water pumps), new serp belts and inevitably, thermostats.
Just an alternative view ?
