pufferman, no doubt about it, I think frozen foods are a much better diet than anything live as well. However, I was speaking on my own personal experience when telling Coankas to try black worms every now and then because if it were me, I would be a bit worried about a Valentini in a reef tank. I am always noticing my puffers picking at the live rock in the tank. They just have that type of mouth to do so.
Also, my puffers, though they like frozen food as well, never really get full off of it and are always hunting for more food when I put frozen in there. I notice that they'll pick at the rocks a lot when they are looking for more food too. However, I've noticed that when I put live blackworms in there, they become pretty full and a little less of pickers and hunters.
As to the ghost shrimp suggestion, while I do agree that they contain some good nutrition for the fish's diet, it seems to me that adding something like a shrimp into the tank just makes the fish more aggressive. I am not trying to be hypocritical. I do add shrimp into my tank, but my tankmakes can handle a little more aggression from each other. Making Coankas' puffer more aggressive though by adding shrimp for him to chase all day isn't always the greatest idea in my opinion because like he said, he was worried about his elibi angel and puffer living peacefully.
I am not trying to argue pufferman. This is just my opinion and experience with this particular situation.