The idea that USD forks are needed to eliminate wobble is a bit absurd. Proper maintenance is all that is required. I've heard of maybe 2 cases of an incurable wobble but that is very rare. Makes sure the steering stem bearings are in good shape. its surprising how they can feel OK but after you remove the front wheel, brakes, etc....you may notice a notchy feeling that was masked when the other components were installed. Not sure why the weight makes a difference but, it does.
Check wheel bearings for play.
Remove rear wheel, differential, and shocks and check the swingarm bearings. The arm should move smoothly and free but have no side to side slop.
USD are are huge improvement over stock. I would not consider them a huge improvement over properly setup stock with aftermarket springs. Don't get me wrong, there is a difference. You pay a lot for that difference though.
I've had stock, stock with aftermarket springs, stock with springs and intiminators, and usd with springs and revalved for the max. The usd is best but the stock with springs was good, much better than stock, and affordable. The bike did what I neede it to do without issue. My usd setup has amazing brakes though!