Ride quality even worse than expected. Advice welcome.

I'm not knocking the well handLing car, that's what I built for myself.

That said, just because someone MAKES huge springs for your car doesn't mean you NEED huge springs (or anything else) for your car. If you make it, someone, somewhere, is gonna buy it whether they need it or not.

Have you stroked your shocks to see if they're smooth and balanced? The jounce bumper is, as mentioned, a good place to start for harsh ride but here's a fun fact: if your jounce bumper is bottoming, all those handling mods are an absolute waste of time and money, so let's hope that's not the case. Bottomed suspension equals slide off road during corner and indicates a fundamental misunderstanding of suspension function.