For me, any premium fare is about space. For economy+, I'm looking for more leg and shoulder room (both BA and VS do this, BD does not, only standard seat width). A dedicated check-in is also good, but my FF status normally negates the need for this - the same for lounge access. However, I don't think lounge access should be provided for economy+: you can buy 3rd party lounges for around £15 if you really want it - the airline lounges are already full enough.
I'd like power at my seat. Upgraded food, drink and other entertainment are a plus, not a need. BA give you upgraded IFE, but it still does not beat the best VS system in regular economy.
For the UK carriers, I think VS have got it about right, BA could be there with the check-in and BD are lagging behind.