> swfdec is [...] roughly equivalent to Gnash in terms of [...] compatibility [...]
> in the current state, Gnash wouldn't give better results.

The last Swfdec version is 0.8.4 from December 2008. Since then, Gnash went from 0.8.4 (what a coincidence) to 0.8.9 in March 2011. I can't really believe that Gnash hasn't generally improved in compatibility over the stalled Swfdec project.
Btw, what about replacing Swfdec by Lightspark? Still an option? It seems Lightspark and Gnash go hand in hand these days with Lightspark executing ActionScript 3 and falling back to Gnash for execution of ActionScript 1 and 2.