Great questions and advice from those in the know and some well meaning but not quite in the know arena as well.
My experience leads me to post a few observations worked out over a very long time of playing around with suspensions though I still seek expert advice regularly of course, nobody knows it all
On this car:
1) Dampers and spring setup for lively handling but not great in daily driving and a bit soft in spring rate.
2) 17" heavy wheels resulting in very short sidewalls and higher levels of energy for the suspension to deal with.
3) Budget, they could of done much better without a big investment at their level of purchasing power.
In general:
1) Better spring to damper rates with stiffer springs can work incredibly well in more situations.
2) Linear springs are better for handling, progressive springs are for ride and not bottoming out, when they compress to a point they suddenly get to stiff, not a good thing.
3) Lighter weight wheels will improve all aspects of handling, ride comfort, noise induced and cause less wear on the whole chassis, a bit less turn in feel can easily be surpassed in real performance gain due to increased grip in most if not all situations.
Experience on this car with BC coilovers:
1) "race springs" originally used, 5/4k rates, rears were progressive and allowed the car to hit pretty hard over freeway overpasses and other large changes at speed, the rest of the time worked great and even helped rotate the car jumping curbs on track at far higher speeds than anyone should attempt on public roads.
2) 8/7k Swift spring upgrade with linear rears, actually rides better most of the time and takes those overpasses much smoother but we sure do feel them, hugely better than stock ride.
3) I might of been better to try 8/6 or even 9/7 rates but overall very pleased with the 8/7s and they will be better on track and require less curb pounding(which is a bit sad as love to jump them
4) 17 OEM wheels are simply to heavy for the car but 17" 16.8 lb wheels with Mich PS3/A/S tires still rode like a brick and very noisy.
5) 15" wheels with summer, all season and track setups all ride hugely better, far quieter, far more grip, less cost though I would of likely ran 16x8 wheels if they were available for less than crazy prices.
Budget minded priority list:
1) A bit of a toss up, better dampers or lighter 15 or 16" wheels and tires, dampers cost less so might try them first.
2) Whatever I did not do first above.
3) Both of the above.
4) Coilovers and wheels and tires.