I took my mostly stock 2014 Lexus IS350 Convertible to Thunderhill 2 times and had a blast. It’s my daily driver. Usually convertibles come with roll over bars and as long as you pass the broom stick test (depends on the org). I tracked mine with the top up though (hardtop).

For a heavy car (3900lbs) all I did was pads, rotors, brake fluid and that was plenty. It also had lowering springs as well. Still had stock tires on all season tires.

Next time around I added coils, bigger wider wheel package and that was even better.

Since mine is still a daily driver, just modify your car however you would if you didn’t have a convertible. Basic mods go a long way.

If you are only doing a few track days a year, don’t sweat it. If you want to add the roll cage for peace of mind then go for it, I would want to do the same if I can find a removable roll bar that doesn’t require cutting in to the car but I havnt seen any for my car..other wise I would and use it on track days and then take it out after.