Sorry to be suggesting something way off-beat here - but I think this has to be worth a go.
If you reduce the weight of the wheels, you'll reduce the unsprung mass, which means every time you hit a bump, the suspension will have less work to do in controlling the movement of the wheel. If you are trying to achieve a ride quality improvement over poor surfaces, I think it would be worth arranging to borrow some lightweight racing wheels from a specialist just to feel the difference and decide whether this is a worthwhile avenue to pursue. Also, you'll want 16" rather than 17", so you get a bit more sidewall compliance.
A typical stylish 17" wheel is 17kg and a typical racing wheel is 8kg. Often, wheels with smaller holes (which look like more metal!) are lighter because the alloy can be made thinner, but there are exceptions like OZ wheels.
I'd like OZ Ultraleggeras myself but not sure where to find them and get them sent to NZ or ZA...
I'm not even sure if they're available in 5x98PCD and 16"x6.5.
Beyond this it would be nice to reduce the mass of the brake discs (big ventilated discs are verrrry heavy!) but the only way to do that is with carbon ceramics as Porsche use.
Of course, 'trick' shock absorbers and just the right combination of springs/shocks will achieve a smoother ride as well, but I can't help noticing that the best-riding new cars tend to have the lightest/least stylish wheels. Think Honda Civic Hybrid, for example...