What will you do about me subscribing for 1 month and simply downloading (or printing) all 800 articles, so I can read everything offline the rest of the year? And even if you can prevent this, how is it fair that a fast reader or someone with a lot of time on his hands gets more content than someone else?
I think it's a good idea to offer the content online. However, I don't really like these kind of subscriptions. Why not have members actually pay for the content you offer? Additionally, I would think it's fair to ask for a (relatively small) monthly fee for the bandwidth and service.
So, if someone subscribes to the paper version, I would expect you get access to the online version of the issues you have received. Similarly, let members buy additional "online magazines" for a reduced rate (you don't have the cost of printing it after all).
An answer to the poll I don't really have. During the holidays I might get enough value out of it to pay 20 pounds, but in general: of course not!