Yeah, you need to tell your insurance company. It's not the fact that springs will cause accidents, but it's an actual MODIFICATION. HEAPS of Insurance companys see modfications as risk, more modifications, more risk to dragging, speeding ect. I know it doesn't have anything to affect the speed of the car, but Insurance companys just generally make an assumption.
Reason why say, Suburu WRX Car's Insurances are way more expensive in Insurance then an Holden Astra, is because people in Suburu WRX's have more accidents = more risk then say the average person who drives as Holden Astra.