spacers: If you are taking off the intake manifold, you might as well do them. they can't hurt.

tgv deletes: not sure about the actual power figure, but if youve seen them in person they are quite restrictive. A stock STI really doesn't need 100% of the air the intake manifold can send through, so its not really an issue. However, the more power you make, the more it turns them into a limiting factor. I had mine removed because one of them failed. It's a good idea to take them out before they do some damage, so I would personally recommend them.