I guess it depends upon whether there are many nymphs in the ponds or lakes. I'm guessing if the wooly bugger quit working most nymphs wouldn't do much better. What you want is as much lifelike movement as possible without having to move the fly very much. Most nymphs (note the MOST) have less built in action than a well tied bugger. What do the gear guys use? Finding that out might give you some clues as to which direction you'll go. When water temps were below 50*F I used to rely a lot on jig and pork rind eels. It became a case of almost vertical presentation. A good start would be to find out what they do (at least if they're reasonably successful) and try to copy their approach with a fly.
Don't discount the possibility that it isn't the fly you're using, but that the fish have changed locations. If you're fishing the same shoreline brush, for example, that worked in the fall, they may have moved to deeper water.