It would be more worthwhile to those who don't already have Sky if they aired more than just F1+support races.
Stick on Indycars, NASCAR and try get the rights to WRC, WTCC...as many motorsports as possible. Then maybe it would be worth it.
Sky is not just Sky though. There's no Virgin cable where I am, and Freeview reception is non-existant, so the only way I can get any sort of TV is through a dish and, as we needed phone and broadband too, Sky was the only option.
My Sky TV package was the lowest one you can get plus I paid £1 a month to get the news package (which, bizarely, included both Eurosports.) Last season, in addition to the terrestrial motorsports (F1 & BTCC), I watched World GT1, European GT3, Aussie V8s, WTCC, GP3, GP2, Porsche Carrera cup, F2, WRC, ILMC (including Le Mans), V8 superstars, British and Italian F3, and probably a few more that I've forgotten, all through either Motors TV or Eurosport UK, (or Bloomberg in the case of the GT1s.)
Motors TV are showing the NASCAR nationwide cup this year too.
This season, I've payed another £10 per month to get the HD package which includes the F1 HD channel. GP2 & 3 may transfer exclusively to that (I don't know if Eurosport will still be showing them as they did last year) but all the others are still available for "free."
For a guy like myself who loves watching motor racing, the best thing about the Sky package is Motors TV and Eurosport, not really any of the Sky channels.