I think it depends on what kind of movies you're looking to be making. If such a pack will fit into your plans and if you need everything the pack includes, then go for it. The other option would be to purchase
Direct Access Points and just pick and choose pieces of the pack that you want through BackStage.
An essential add on for me is
3DXchange - if it isn't bundled with your iClone purchase wait until after you've bought iClone, go into your account and there should be a $20 discount for it). With it you can import an immense number of free models via Google 3D Warehouse or other compatible 3D models.
Another must have pack is the
G3 Clone Cloth - both for Man and Woman (you can get the two together for $160 - I'm not sure what that is in pounds). With this pack, you can design your own clothing as well as take advantage of some of the clothing freebies available (most freebies so far were designed for the G2 Clone Cloth). I think this is essential for diversifying the look of your characters.
Hope this helps some!
Oh, and please don't forget - there are lots of freebies available.
CoolClones is a great forum that offers a ton of them as well as a place you can ask for help. :)