capacitor choice for CVcore - is the recommended 470nF value critical?

A too-low capacitance won't provide enough charge to keep the core voltage stable during sudden power consumption changes. If the capacitance is too high, the voltage regulator might be not capable of charging the capacitor fast enough if necessary or overshooting the destination voltage will last longer. Both conditions may cause increased power consumption (especially if core voltage is decreased during LPMs) and may cause device failure if too extreme.

Also, the datasheet tells that the capacitance on VCC should be at least ten times the Vcore capacitance.

Yes, 470nF is a fairly uncommon value. But it is a rather calculated value. 100nF, however, is just a common capacitance to suppress ESD and line 'ringing', not for really buffering a charge. While 1uF is good as a small local charge buffer but might be too large for the low-power fast-response requirements of the Vcore regulator.

If you need low power consumption, you shouldn't save money on cheap Vcore buffering. You need low ESR low leakage capacitors for this task.