AFAIK the lounge at Crewe is classed as the "Cheshire Lounge" and, uniquely, is open to holders of ANY First Class ticket which is routed to / from or via Crewe. So it is not limited to holders of Virgin only tickets.
This used to be explained on Virgin's website, so I assume it still applies.
One thing that I always think is ridiculous: someone paying, say, over £100 for an Advance ticket from Leeds to London will be refused access to the Lounge at Leeds (or will now be able to pay the £5 supplement, but once upon the time this was not the case), whereas if he/she holds a First Anytime Single to Wakefield, at a cost of £3.60-ish, can have access!
I certainly made use of the Leeds Lounge on more than one occasion with a First Class single to Bradford, in the days when there was an 18.05 departure from Leeds to Forster Square. I got a few raised eyebrows from the Lounge staff, but they couldn't say no. Then when I boarded the train, because it was usually a London crew, they weren't in the usual hurry to get cleared up, so it was tea and biscuits on the train too! All for about £2.60 single, ah those were the days...
Wouldn't it be more sensible to just have a minimum fare paid for entry to the Lounge, irrespective of type of First Class ticket held? It is one of the (very) few benefits of travelling with Virgin, in that the Lounges can be used with Advance tickets, and there doesn't seem to be any restriction on the length of time that one is permitted to be in the Lounge, well, not at Euston anyway.