I cannot comment on some points, but can on others given my older 2350 and the 2552, both without a slideout, will have some common features.
I think the 2552 comes with a free-standing euro chair placed behind the passenger seat. Am I right?
If so, you can request a 3rd captain seat, identical to the ones used up front. The only real advantage is that the seat is bolted to the floor and has seat belts, safe for a 3rd person to travel in. Here are some pictures of my wife modeling our 3rd captain seat in our NO-slide with dinette 2350.
As Tom mentioned, slide outs are extremely popular, so I won't get into why we are very happy with our decision in not getting the slideout in our 2350. I will say that back in 2007 when we bought ours, the slideout was much smaller which I could not see enough benefit unless you needed the couch with fold-out queen bed to sleep 2 more people.
In recent years the fridge has been included in the slideout which makes the interior much more roomier than it used to. And in the 2552 you get a pull-out pantry next to the fridge when you get the couch, which is a very nice extra feature as shown here.
Looking at the floorplan of the 2552 with dinette in a slide-out, you give up the pantry to maintain good leg room and large table. I would assume then a dinette without a slide-out would re-introduce a pantry when you consider the dinette is then moved farther forward about a foot closer to the driver like we have as shown here. You further gain wall space by deleting the slide-out walls & related wood trim. Maybe the pantry gets near 2 feet wide.
I wonder if all other models with the dinette booth in a slide-out would be cramped as shown here in this older model that does not include the fridge.
For comparison, this is our NO Slide-out dinette. It also demonstrates how one can sit anywhere on the front facing booth and watch TV when traveling as well as when parked. One of us will lean against the outside wall with a pillow to get comfortable while the other takes the captain seat.
It would be interesting to see some dinette booth pics and dimensions in the larger slide-out in the 2350, 2551, and 2552