Nicky as always has been played a role as a sweet, innocent role who often doesn't get in trouble. However they had to ruin it in Season 3 when he made up the Meh-Guy. Also his reasons didn't make sense to why he told that his reviews need to be 'honest' when he hasn't been honest to them anyhow.
Ricky has lost his intelligence. If you remember about when they thought one of them wasn't a real quad. I mean who would think someone isn't related to them because of what their preferences are. I was shocked when he thought of the reasons why he didn't think Dicky wasn't a Quad. The other 3 reasons were more accurate than his.
Dicky was the closest and he is the dim-witted of the quad. Also I think he has lost his vain personality. He no longer talks about his good hair. Also, is less romantic.
I don't agree with your assessment. Here are my counter-arguments:
Nicky has always been manipulative and it's been shown since the beginning that he just pretends to be innocent. This was first explored in Remote Control Control where he manipulated the other quads so that he can have the remote. As for his reviews being honest, journalists, reviewers and writers who respect their work are required to write in honesty and without bias. That doesn't mean they are not dishonest with other things in life.
Ricky's assessment about who shouldn't be one of the quads is actually the more biologically accurate one. Related people / People with the same genes tend to have similar preferences. Dicky's argument was that Dawn can't be related to them because she's a girl. That was the dumbest argument.
Dicky reducing his vain personality and talking less about his hair and not trying to date every girl he meets is called character growth. As you write a show, characters have to grow and change. If they remain the same as they were 3 years ago, then you miss character development and it's just bad writing.
Dawn being goofy and jealous is still pretty much as it was in season 1 and 2. Her jealousy usually seen with being overprotective of Mae and trying to take down Ricky has been pretty much the same since the beginning.
Season 3 is actually the season with the best flows not just within an episode but across multiple episodes. A lot of storylines are continued in several episodes.
Honestly, to me, if you want to see a season that doesn't flow, look at the last 12 episodes of season 4. They have almost no relation and really kinda let me down for the end of a show. I definitely liked the other seasons much better and really enjoyed season 3. I do like that the characters are more grown up in season 4, but without Dicky at the end and all the quads kinda getting really jealous in general, season 4 did not have "flow" to me. What do you guys think?