As long as that voucher is truly a cashlike instrument valid at any Marriott in the world under any circumstances, I'd probably just accept it and be done with it. Your compensation for your troubles is a few extra Marriott points, assuming you will indeed use the voucher quickly.

But the hotel messed up here - you used your EEO properly. If the voucher comes with more strings attached, such as a requirement to buy up to a higher rate (like Bonus Bucks and EEOs essentially do), or a prohibition on using it on a future two-night EEO stay or with a Bonus Buck, then it's not really an equal trade.

My I'm nitpicking: I get worried when I see "voucher" because the legalese can restrict it. Gift cards or gift certificates are typically regulated by law - it's much more difficult for a business to sell a gift card and then later attach caveats to it that limit it to only high-margin merchandise (like forcing you to buy up to a higher rate for a hotel room).