Bouazza, 22, signed a four-year deal at Fulham - but Boothroyd believes the Algeria international forward has made a mistake in leaving the Hornets.
"Hameur wouldn't necessarily have been a starter," said Boothroyd. "If everyone had been fit, [Tommy] Smith and [Jobi] McAnuff would have started.
"We had a player who I didn't think was anywhere near ready to move. He should have stayed a little bit longer, to grow and develop.
"But the lure of the Premier League, and the money to be made by all concerned, is a heavy burden sometimes.
"I have a lot of respect for Hameur, for where he has come from and what he has done.
"But if a player is so desperate to go, you have to weigh up his effect on the environment.
"To get £4million for him is probably good business, considering I was going to move him on if he hadn't done anything after coming back from Swindon (where Bouazza had a loan spell towards the end of the 2005-06 season)."