Here's an effective trick that I've used with lots of low spoiler cars (including my really low Ferrari). Park your car a safe distance from the tire stop or any cruncher you are trying to avoid (keep moving car up until you are satisfied with the clearance). Get back in the car and assume the normal driving position. Now just turn your head to look out at the right hand rearview mirror. Note where the next curb over is with respect to your mirror. For me its right under the bottom of the mirror. Now when I park, I just look over under the right mirror until I see the curb or (whatever) just "touch" the bottom and I'm automatically a save distance from the obstruction. Try it, with practice you'll be a pro. Obviously, it only works if the right hand parking space is empty!