I'd be pretty peeved too Aberdeen BA Traveller. The £5 voucher is ridiculous and you won't get much for that in the airport. I'd definitely complain to BA - be interesting to see what their response is but I imagine it'll be along the lines of "Thanks for your email.....we note your concerns.....your custom is important to us......blah blah".
As an aside, the Northern Lights lounge is great so if you do feel like shelling out to get lounge access while the BA lounge is closed, it's worth it.