Car insurance

Omnium insurance is based on the full value of the car depreciated over time. My insurer assured the full value of the car (from new) for the first 18 months and then depreciated the car's value by 1% per month - so that at five years old exactly it was worth (for insurance purposes) 58% of the full value that it had when new.

I would guess that most insurance companies use a similar if not absolutely identical depreciation rate. Note that the premiums did not reduce in step with the depreciation in the value of the car so I imagine that full omnium taken out when the car is already five years old will be based on 100% of its new value not, stay, 58%, so you may well find the premiums almost unaffordable.

Yes

You will pay the premium on the full value but in case of total loss will only be paid a reduced value. For all partial losses, you will be supplied with new parts (hence the premium on the full value).

You might be requested to have a survey of the car at your expenses before inception as the insurer will not want to pay existing damages.

The question is then....is it worth it ?

Yes, it is