It’d be safer, but it wouldn’t be very comfortable. Rally cars have very barebones interiors to cut down on weight. You’d also need different tires and tuning.

It would be better able to handle a severe crash, but pretty inconvenient and pointless.

You can put a full and spec cage, bucket seats, and a 5 point harness in any car. You don't need to go full racecar and take the interior out. You would need to wear a helmet, Hans device, and the full 5-point every time you drive the car because an otherwise survivable accident could kill you. You would also probably want a fire suppression system because a fire in a damaged car may not be escapable after you get hit without help.

You would be giving up airbags and visibility. Airbags can save you as much as a cage could. Visibility could prevent the accident in the first place. The cage and whatnot wouldn't save you from a catastrophic wreck, but a serious accident would be more survivable.

You might as well just not drive on the highway or don't get in a car at all if you are so concerned about your safety. Don't want a baby, use protection. Terrified about having a baby and don't think that protection is adequate, get sterilized or don't fuck.