I will pipe in with my 2p worth.
What you value your (on the road 110) is what you value it at, if you feel you are undervaluing it then you need to tell your insurance. So keeping an eye on todays values is fine.
But. You are talking about...
Welcome to LZ.
I would be wary of over gearing it as you could end up with a 4 speed car as fifth will be unusable on anything that resembles a hill.
Considered an overdrive?
On the other hand ear plugs are dirt cheap.
I got the 12k for mine after the fire from the insurance with no arguments, but that was 3 years ago now.
I completely agree with your comment about we spend too much on them without increasing the value. I have no intention of ever selling mine...