Well - I already own ARC 2, so (as far as I know) I only have to "update" to the new MEMS microphone.
The price for that new microphone does not seem too steep (€84.69 Incl. VAT). However, as I live in The Netherlands, I am afraid the shipping cost will be "substantial". I could not find a local dealer that sells this microphone separately (they only sell the "full" package including software).
The website from IK Multimedia does not give any shipping costs beforehand, so I am reluctant to place an order. I guess I will hold off for now, until I know if it is really worth the money to update.