Are there fans for radiators to improve performance?
An alternative that might work in some rooms is a ceiling fan that has a low speed (we have some 6-speed models in our home where the lowest speed just circulates the air slightly).   This would help move air around in the room (and thereby helping to move some heat away from the radiators) and has the added plus that you can use it on higher speeds for summer cooling.

We have forced hot air heat, and our master and living room have high ceilings, so we run the fans year-round.