I've flown both CO and VS several times and my opinion is that while I'm a loyal CO customer, the VS product experience was superior overall and may be worth the extra $$ for the following reasons:

1) The service handling on the ground was exceptional. In particular the limo service was the best for me and my colleague because we didn't have to deal with any hassle in getting to our destination. In addition, they picked us up for our return to LHR, we were checked in and given our boarding passes and there was literally no waiting for any security. We walked right through with no hassle. That was very well worth it for us.

2) The LHR VS Clubhouse is an extraordinary experience. It allows you to get a full meal before your flight and the salon offerings/massage/etc is great.

3) I don't sleep on flights so I'm impartial to the VS lie flat seats or non-lie flat that CO has. CO has a wider seat which is better for me, but the diagonal layout on VS allows you to not be disturbed by other passengers who may need to move around throughout the flight.

Overall, we actually paid less for the VS flight than the CO flight as CO appears to charge a premium on the codeshare it seems. We saved just over $4,000 for two people on the VS coded flight than if we'd purchased it through CO. So it was a great deal.