Difference in value! Two identical cars side by side how much cheaper would the one with the dvla vin number compared to the one with the original tag.

I'm just about to start getting mine up to scratch by having a full re-spray, but wasn't sure if it would be financially worth doing? It's a solid car with all original rot free panels with a little bit of rust by the sunroof and in the engine bay in a couple of places, but the paint lets it down, it's sat for six yrs due to life situations and I'm now at the point to get it sorted and use the bloody thing.