I had the same issue on my 02 b6 a4 3.0 - eventually both arms of the change-over mechanism snapped and the rotary valve was stuck on the long intake tract. From my experience, dealers will either charge you >$560 for that part or make you buy a whole new intake manifold ('bout $1,300). No way.

I eventually totally ripped out the rotary valve, leaving the manifold hollow. Theoretically, this would hinder induction by permitting destructive interference and causing harmonic and volumetric imbalances between cylinders. Personally, I have to say, there's no real noticeable difference. If I had to say something, I'd say there's a small improvement in pull >5000 rpm, and a very slight loss of torque between 3-4k rpms, but it's soooooooooooo slight that it's possibly all psychological. There's no check engine light or anything - the car runs as smooth as ever, fuel economy is normal (and I've been using this as a daily driver for quite some time).

Honestly, I can't imagine the vehicle performing much better, even if the manifold was fully operational. If the day comes when I buy a new actuator assembly or somehow repair the old one, I'll be here to confirm. But until then, I wouldn't make fixing this a huge priority.

Of course, it is possible that my car was just so FUBAR to begin with that this one little thing makes no relative difference. Food for thought.