You are confusing liability with property coverage. The 100/300/100 or $500 CSL you mention are liability limits which cover you should you hit someone else.
The car itself is insured to ACV=Actual cash value. You have modified this to include $2100 additional aftermarket work.
As respect your deductible of $250. That's too low. Being a P85 owner I am guessing a $2000 fender bender repair will not set you back financially and you would rather fix it yourself than deal with your insurance co. Therefore you should raise your deductible to say $2,500. Use any saved premiums to buy higher liability limits.
+1
Obviously "peace of mind" is worth different things to different people... personally, peace of mind is the last thing I feel when I get the sense I'm being ripped off...