Hi, I've got an old Viking myself, which will be pressed into use as a winter bike again this year. Vikings can be difficult to pin an age to. I found out mine was a 1961 (probably) because that year was stamped on the back of the brake arm. (they were centre pulls, ). You might be able to find out more by googling classic lightweights or classic rendezvous, 2 websites devoted to cycles of around that era.
Some Vikings were (and still are) desirable, but even the run of the mill older models, like the 'mile eater' I suspect mine to be, rode well and were well made.
I suspect yours will be a 60s/70's model, and at first glance looks to have been pretty well cared for.
regarding value, they aren't amongst the most treasured of marques, mine cost me a tenner a few years back, you might get more if you sell it in a city as a vintage fixed gear project
On the other hand a hand made lightweight frame with fancy lugs like that would cost well over a grand today, and as long as its straight and true I bet it rides as nicely as anything... you can never have too many bikes can you?!
