If you lower with the torsion bar adjusters, you will probably need to replace the stock torsion bars with larger diameter (higher spring rate) bars. Any significant lowering with the stock torsion bars will cause your suspension to bottom out on the bump stops, as there won't be enough available suspension travel left to handle any bumps. Your spring rate has to "match up" with the amount of suspension travel you have. The lower you make the car, the less suspension travel you have before the suspension will start to bottom out, and the higher the spring rate has to be to keep from bottoming out the car. The stock torsion bar spring rates are barely enough to deal with the the amount of available suspension travel at the stock ride height, so, when you lower you pretty much always need to upgrade the torsion bars (or constantly bottom out the suspension).And of course, if you lower any significant amount with the torsion bar adjusters you'll need a new alignment.
If you don't want to buy new torsion bars (and better shocks to handle the higher rate bars so your ride quality doesn't go to hell), you can use drop spindles. They have drawbacks too though, even outside of their high price. They generally make the suspension geometry worse than a car that's lowered with the torsion bar adjusters. Bump steer is worse in comparison, roll centers are better on cars lowered with the torsion bar adjusters (has to do with control arm angles), camber gain is better on cars lowered with the adjusters, etc. The also tend to make rim clearance more problematic for larger diameter wheels, with standard spindles 18" rims clear the outer tie rods so more backspace can be used for wider tires, but with drop spindles the outer tie rod clearance is an issue again. For smaller wheel diameters you still have to deal with the outer tie rod so not much changes, but some of those suspension to wheel clearances are different so you do have to check.
