I heard that Osiris and Warmind were pretty disappointing so I gotta say I'm not itching to drop the cash on those...
If you don't really care about playing CoO and Warmind then you might want to just wait for the complete bundle with Forsaken + D2 + both DLCs to drop. Bungie tweeted yesterday and said more pricing options would be available closer to launch, so you'd just have to wait a while before you could get it.
CoO is pretty awful but you can run through the story missions in about two hours or so. Same with Warmind though the surrounding content in Warmind is a little better. Really just depends on when/if you plan on catching up so that you're ready to go for Forsaken. They're required to play Forsaken regardless.