I have a 92 e36, I have full cover on mine,
The insurance company reffered to their statistics and said they feel my car is only worth $7.5K NZD, i paid a little more than that because it was lowered on bilsteins and has some nice wheels too.
I told them i wasn't happy with 7.5K so they said if i want to do an agreed value i would have to get it valued. i got it valued for $9.7K NZD and its fully insured for that (no under 25's) its around 450-500 a year to insure, and the excess is pretty low too.
It comes down to what you're willing to pay for yourself.
No insurance - you pay for everything that may be a consequence to you having an accident.
3rd party - covers you damaging someone elses property,
then theres 3rd party plus fire theft vandilism - which is fine for most things but if you're car is a write off its not covered.
then you have full comprehensive. - everything is covered, even the windshield. and of course if your car is written off you get paid out.