I really don't see how Freddy is that much goofier acting in 4 or 5 than he was in part 3.
Let's compare then.
A Nightmare On Elm Street 3: The Dream Warriors
1) Philip is turned into a marionette and walked up into the tower where Freddy was conceived, then the strings were cut and he fell to his death. No one liners or bad puns.
2) Freddy pops out of the top of the TV, grabs Jennifer, then says "This is it Jennifer! Your big break in TV! Welcome to prime time, b**ch!" Then he shoves her head into the TV.
3) Freddy disguises himself as the hot blonde nurse Joey has a crush on to lure him away from the others. Then as they're making out, Freddy's tongue flies from his mouth and ties Joey spread eagle to the bed frame, to which he says "What's the matter Joey? Feeling tongue tied?"
4) Freddy chases the cripple with a killer wheel chair. Then when the kid tries to use D&D magic to banish Freddy, he says "Sorry kid, I don't believe in fairy tales", then stabs him with his glove.
5) After a brief knife fight with the Taryn girl, Freddy turns his fingers into syringes and says "Let's get high". Then after he kills her by a drug overdose he says "What a rush".
6) Freddy's animated skeleton throws Nancy's dad through the air and impales him on the rear fin of an old automobile (I think it was a Cadillac). His skeleton then bashes Neil with a shovel and starts burying him alive.
7) Freddy impersonates Nancy's father in order to get close enough to kill her. When he reveals himself to actually be Freddy and stabs her in the gut, he says "Die b**ch!"
A Nightmare On Elm Street 4: The Dream Master
1) Freddy stabs Kincaid in the gut after waking up in the junkyard. Kincaid says "I'll see you in Hell," to which Freddy responds "Tell them Freddy sent you."
2) Joey's dreaming about a naked girl swimming around in his water bed. Then Freddy pops up and says "Hey Joey! How's this for a wet dream!" then kills him, causing his body to somehow be trapped INSIDE the bladder of his water bed.
3) Kristen dreams herself to a beach where she believes she'll be safe from Freddy. Freddy uses his blades as the fin of a shark and goes right up to the sand castle which he causes to explode, revealing himself. Then as Kristen is being sucked down by quicksand, Freddy puts on a pair of shades before pushing her down. Then he kills her in the boiler room by throwing her into the burning furnace.
4) Freddy locks the class brain into her desk during an exam. Then he walks up to her and says "Wanna suck face?" before sucking the life out of her.
5) Freddy kills Alice's brother Rick by invisibly attacking him in a dojo, mocking him with taunts about how "A ninja warrior doesn't need to see his enemies to defeat them" and that "A ninja warrior must have balance."
6) As Alice is dreaming that she's in a diner, Freddy sits down next to her. "If the food here doesn't kill you, the service sure will" He's served a pizza with the souls of all his victims baked in as meatballs. "I just love soul food!" Stabs Alice's brother in the face. "Rick you little meatball!"
7) Freddy kills Debra by turning her into a cockroach, trapping her in a roach motel, and right before he crushes her he says "You can check in but you can't check out!"
8) When Alice's boyfriend is being sedated so he can be operated on, he dreams Freddy is in the operating room. He shouts "Krueger!" to which Freddy replies "Well it ain't Doctor Seus!"
There might be some more examples that I'm missing, but for the most part I think it's fairly obvious that Freddy was sliding far more to the side of silly in Part 4 than he was in Part 3.