With Johnson also the top scorer in Division One last season, the decision to allow him to leave St Andrew's looks questionable in hindsight.
The Birmingham manager said: "He's been a fantastic success for them and will be one of the main threats against us.
"He had a remarkable time last year and it looks like he is carrying on this season.
"I am not surprised by how well he has done. One thing you can always say about AJ is that he has great enthusiasm and a great work ethic.
"He is very athletic and direct and it is fair to say that I'm pleased for him even though I could do with someone like him at the moment."
Johnson was undoubtedly a bargain for Palace. His cost has been recorded as £750,000 as part of the £4.25million deal which took Morrison to Birmingham.
Palace manager Dowie says it is impossible to put too high a value on him now and believes he has the potential to play for England.
"I thought at the time Clinton would give us a better option," said Bruce.
"AJ could not get in the Birmingham team because we had Geoff Horsfield and Stern John, who ultimately took us into the Premier League.
"His options were going to be limited and he decided he needed to go away somewhere and play.
"Sometimes players need a change. He came to Birmingham as a 14-year-old and he needed to go away and make a name for himself, and he has done that.
"He has got nothing to prove coming back here at all.
"It is always something special when you play against your old club and I am sure he is looking forward to it.
"I think the Birmingham fans will give him a decent reception because he came through the ranks and always gave his all for the club."
Another player who gives his all for City is Robbie Savage. He will return to their side tomorrow for an interesting midfield confrontation with former Birmingham player Michael Hughes, providing the Irishman recovers from a hamstring injury.
Both were sent off after clashing in the 2-2 World Cup qualifier draw between Wales and Northern Ireland last month.
Savage left the Millennium Stadium pitch in tears and said the resulting ban, which meant he missed Wales's match with England, was the biggest disappointment of his career.
Birmingham should have Muzzy Izzet (knee) and Stan Lazaridis (calf) available but Mikael Forssell and Morrison (both knee) are ruled out.
Sandor Torghelle is suspended for Palace and Dowie will give late fitness tests to Hughes and Fitz Hall (knee).
Birmingham v Crystal Palace, St Andrew's, tomorrow, 12.45pm (Live on Prem Plus)
