Shock absorbers Bilstein or KONI

I put Bilstein on the front of my BMW and KYB on the rear and the car drives like a new one.

In my experience shopping for a miata, generally there isn't a huge difference in value between all-stock and "OEM+" cars that have minor tasteful mods from reputable companies. Koni and billstein shocks are pretty common and may even help resale a little bit. Repairing worn-out parts with slightly better aftermarket replacements doesn't hurt either. Any car with new bushings (provided they are rubber and not poly) will probably be preferred to one with the original, whether they're OEM or the slightly stiffer IL Motorsports ones that are common. Ditto for things like bump stops, shock mounts, et cetera.

I totaled my beloved 2020, and got a 2021 recently, the only difference being the Bilsteins to lift, still setup by Primitive Racing. I immediately broke myself to get all the same stuff as the 2020.

I did it myself with Bilstein 5100s, cost about $700 and gave my truck a 2.5” lift. Looks awesome.

Bilstein B4 is a good replacement.

Front struts were making some noise so, I got some bilstien 5100 for front and back. Definitely worth the $ to upgrade. Also you have the option to add up to 2.5 inch’s off lift in the front with bilstien ride height adjust.

I have the yellow Koni with Progress springs. The ride is good, just a little bit lower than stock and still useable with our crappy roads and speed bumps. The yellows don’t have height adjust, but I don’t need that.

I love the Koni Special Actives I put on my 530i daily. Comfortable on the highway, great and control in the twisties.

Bilstein B6 monotube shocks work only with stock ride height springs. With a chassis as light as the IS300, they’ll give you a much stiffer ride than the other options. Some drivers like it; but you may worsen traction on roads in poor condition. Comfort will similarly degrade. Their main advantages are that they won’t fade in prolonged aggressive driving and they last a long time.

B4s will fail after 1-3 years at most.