Smallpilot
Were you given information about the compensation scheme?
Provision of such information is mandatory.
Worth looking to see if this flight was covered by the rules, since if it was, VS may not have done as much as they should have done (i.e. getting you there by another route/airline.)
Also, if the EU rules apply, you should be offered a refund.
Although the computer system was (possibly) beyond Virgin's control (a lawyer would have to take a view on that), the crew going out of hours without a standby crew may not be.
So definitely worth a look..... and I'm sorry that your holiday was ruined.