Every one always talks about what you will get if you have a problem. I understand that thought but if something happens to your modded car that may be the last thing you need to worry about.
Example
Say you buy your Stang for $20,000 and you spend another $20,000. Now your in an accident and the adjuster tells you the car is worth $15,000. That sucks.
But it can look like this
You buy your Stang for $20,000 and you spend another $20,000. Now your in an accident and the adjuster tells you your claim has been denied due to misrepresentation. Your getting $0 and that lady that stopped to fast I front of you? Her neck hurts and she can't work. She is suing you for loss wages and pain and suffering.
So now you've learned your lesson but can't find any insurance company that wants your business be cause of the misrepresentation issue.
The $40,000 you lost on the car can be the small problem here.