> There will be some extra noise on Vcc right at the PIC even with good
> decoupling and this will have the result of inducing some noise into
> your oscillator. As a consequence you can expect some random jitter
> on the clock - this in turn will decrease its spectral purity and
> DECREASE the magnitude of harmonics, instead spreading the noise onto
> other frequencies. The end result MAY be to reduce your EMC peak
> emissions slightly.


How about not radiating significantly in the first place?
Somehow it dosen't seem to me a good idea, to deliberately increase your EMI
in hopes that it will decrease by using dithering the osc. Also, it seems
highly unlikely that you'll be able to pull the xtal by any significant
amount, unless you have HUGE noise on the supplies (volts?)

IOW, If it could be made to work, it would still not work.. :)