If you have mineral oil in your car I would definitely change it. CVH engines, especially the hydraulic tappets, are very sensitive to decent oil and as SpannerJuggler indicates, mineral oils can degrade over time. CVH engines should really have their oil changed every 6k miles anyway, so you're not 'wasting' much anyway.
And if it was me, I'd change the cambelt. It's a simple job and gives great peace of mind. You could even go the extra mile and bung on a vernier camwheel, that way you can set the valve timing up a bit more accurately for those vital few extra horses.
