I'm actually not a fan of the album release format as a standard. Tradition has lead to complacency and thus we are left with an outdated release model. There are albums which make sense because the songs are related or tell a story (Pink Floyd's The Wall, Adele's 21,etc..)
(stepping off soapbox)
I am not sure that I would purchase an album specifically for the extras unless I valued the extras more than the album itself. Added value is one thing but just throwing a bunch of stuff into a package deal isn't compelling unless I see value in the purchase as a whole. Perceived value is personal and will vary with each individual - thing's that I want may not satisfy someone else.
I would like to suggest that you use a system similar to Amazon's suggested add-on's. Give your fans options for example:
Album only ($10)
Album + a sticker ($12)
Album + autographed liner notes ($15)
Album + autographed poster ($20)
Album + Tshirt ($25)
Album + sticker, autographed liner notes/poster, Tshirt ($40 - Save $2)
With this example you are giving them options, and a compelling reason to purchase the largest combination package. What you are avoiding is forcing your customers to make an either or decision (do I pay $40 for an album with a bunch of stuff or do without).