Iberia Plus is offering 30% bonus for Marriott Rewards points to Avios conversions until December 31, 2013.
There are no terms & conditions associated with this offer, but you can access a web page (here) on Iberia’s web site, where this promotion is discussed.
Seems that Travel Packages are not excluded from this conversion bonus (read more about Travel Packages here).
My opinion is that doing a straight conversion of Marriott Rewards points to Iberia Plus Avios makes very little sense. Issuing a Travel Package with Iberia Plus Avios as the partner airline could be worthwhile, however.