I have been thinking about something similar.
My inspiration is Kymatica's parallelport CV / gate interface :
http://www.bitminds.net/kymatica/uploads/Hardware/pc-interface.pdf
He uses a serially controlled MAX536 quad DAC to generate the CV with very high precision.
It should be easy to use Arduino in stead of the parallel port.
The MAX536 is VERY expensive and need quite a lot of external components to work in this scenario, but it can generate 4 CV's at the same time and with the high precision a musical application requires.
Cheaper single channel DAC's could surely be found, but as soon as you require the handeling of 10V with a decent "bit depth" the pricetag just goes up.
MikMo
http://ww.mikmo.dk