One lake in Florida named Lake Panasoffkee is four feet deep. From shoreline to shoreline, all you can see is weeds. It is so clogged with weeds, that fishermen have to drive their powerboats through them to make a clear pathway in order to cast their baits.
So, however clogged your lake is, take heart. My solution would have been to insert a row of four-inch scraper razor blades along the leading edge of the daggerboard (and rudder) . However, even the effort to cut those weeds would have slowed the Sunfish to a crawl.
The existing Sunfish keel is insufficient to avoid leeway in any point of wind, but fiberglassing a full-length two- or three-inch keel "blade" atop it would help. When tacking, you'd have to "wear about", but you'd be sailing.
As I head for deeper water--and faced with weeds captured by the daggerboard, I just raise the board to clear the pulled weeds, and the rudder seems to readily shed them. If racing, be sure to shed those weeds when you're directly ahead of your nearest competitor.
You can raise the daggerboard up some, depending on which direction you are sailing into/with the wind. It only needs to be down far enough to keep you from slipping sideways with the wind. And then, as L&VW mentioned, just raise the board up every so often to clear any accumulated weeds.
There is a lake near me that is chock full of weeds in some parts, I've basically quit sailing there because of it.
(here's a video of me drifting along there, getting stuck in weeds multiple times)
But if you love your lake, I don't imagine that's an option to just find a nearby lake that has less weeds.
Same problem as the Butterfly rudder, it does not float. After
the kids send $250 the bottom of the lake a couple times
you can usually find the Butterfly up for sale on Craigslist.
Then after nobody wants to shell out the extra money for
a rudder assembly the boat parts show up in separate listings.