You’re right about the RX is not a commonly modified model.
Most people who own this car just aren’t interested in performance modifications. That’s because it’s very difficult to improve horsepower without spending a ton, you’ll sacrifice reliability, and there is minimal aftermarket support for RX mods.
If you are desperate to leave behind the smooth, quiet ride from your factory RX350, you could try coilovers. To improve the steering, you could try something like wheel spacers. There are supercharger kits on the market, but you may run into problems with clearance.