Having examined the old kit that recently came off my Old Girl the other week, can say as per the OOF advice, every 40k and 4 years is the time. Mine had been on for approx 8-9 years (7 of those years SORN on the driveway). The pulley felt fine (done approx 27k), but the belt was showing signs of minor cracking all over when flexed. So under normal wear and tear, I'm sure the bearings/pulleys would have started failing after the 40k, but as proved, age does affect rubber, and the 8 years of age on the belt is showing.
As said, it's the bearings that fail. In theory you'd probably be fine leaving your original belt on for 80k... however, you get a belt in with the kit, so literally no point whatsoever in re-using the old belt.
It's the biggest cost on an Omega, approx £400 at a Dealer - but if you want to tackle it yourself (and it's really not a bad job once you've done it, I was surprised how easy it was) the advice on here is second to none. As you have found, under £100 will buy you a kit, half a day set aside will see you back on the road for another 4 years. Call it £25 per year, so not a terrible cost in real terms.