For: Transistor + OST, Bastion + OST. OSTs seem to be only available in mp3 format though (I prefer lossless CD quality).
If you already own 1 or more of the 4 items, Steam will take this into account and automatically offer you a much lower price for the bundle items you lack. This feature seems to be relatively new, and only about 35% of Bundles on Steam don't force you to repurchase content you already own. I am not sure what this is officially called. Dynamic pricing?
Bastion is great, and I assume transistor too. But the annoying thing about this bundle is that you're paying an extra ~$3.60 for the soundtracks even if you have no interest in them.
Better to buy the games individually at 80% off…the extra 2% off one or both of the games isn't worth it unless you want the soundtracks. (you're saving 40c extra on transistor and 30c extra on bastion, vs paying $3.60 for the soundtracks.)