Yes, improved anti-roll stiffness at the back can make a big difference to the feel and roadholding, and is probably the best suspension improvement you can make. I'd do that first, especially if you are looking for better suspension performance.
Lowering, other than for looks, is often counter-productive on the Golf Mk.4 platform as the roll center drops twice as far as the CofG does.
Because of the construction of the standard ARB, you have to add another, separate, one. Several aftermarket suppliers provide kits for it though, the main
problem being where to fit the mounting brackets.