I agree completely that you need to throw in some marginal hands like 7-8s, 8-9s, etc. to keep your opponent off-balance.

I also agree that you may lose some value pre-flop when your opponent might 4-bet with a worse hand. In fact, on some sites you can 6-bet playing heads-up so against a tilting or super aggressive opponent, you really could lose out. So, I guess it's not right to never re-raise pre-flop against these types of opponents.

Against non-tilting or ultra-aggressive opponents, I'm still not sure though. I check-raise a lot of flops as it is with made hands and draws alike so it's nice to add some more deception to my flop play to really keep my opponent guessing.