Fast Healing is rare and expensive... because Wizards grossly overestimated it
In combat, Fast Healing is a very weak variant of Damage Reduction1 or Resistance; instead of reducing every attack, you heal a set amount of HP afterwards. So, assuming the attack doesn’t kill you, FH is effectively equivalent to DR that only works on one attack. Except you could die before you get healed.
Out of combat, Fast Healing is an extremely expensive way to top off between combats. A wand of cure light wounds or wand of lesser vigor accomplishes the same for massively less money. By the time you burn through one, the 750 gp to replace it is chump change. By the time you could afford significant Fast Healing, in most cases, 750 gp could easily be a rounding error.
Even without items, you can get far more reliable healing than that offered by Shadow Creature for less investment. Draconic aura: vigor gives Fast Healing to everyone in your party; it won’t heal them past 50% of their health, but you also get a real class level (read: BAB, HP, Saves, Skills) and it’s only one level (dragon shaman or dragonfire adept) and it affects everyone, not just you.
But nevertheless, most sources of Fast Healing are extremely expensive. The healing blood silthilar graft from Lords of Madness is an utterly obscene 180,000 gp for a mere Fast Healing 3. So from that perspective, LA +2 might look like a good deal. It’s not. LA +2 is a huge cost; it very, very badly hurts you, reducing your most critical numbers (HP, BAB, saving throws, skill ranks) across the board. Fast Healing 2 is close to pointless; it is not even remotely worth LA +2.
- Unless it’s /magic; that’s worthless. Thus, I don’t recommend you take the DR option on Shadow Creature. Any other sort of DR, though, is much much better than FH.