I think the difficulty is that the question is, "What are the best parts to cut out?"
I ran the campaign with my wife and kids (7 and 11), and all three of them remember Scarwall as being the best, most epic, most fun module they've played so far. (And my wife has now done 5 modules of Crimson Throne, 3 modules of RotRL, 2 modules of CC, 1 module of CoT, and 1 module of KM). It is not so much a massive dungeon crawl as a HUGE haunted house with a rich backstory, with every major creature having a tale behind it.
Scarwall was epically fun to run, it took many sessions, and we all remember it fondly. It LOOKS like a giant dungeon crawl, but if you as the GM focus on it as a haunted house, and provide lots of rich spookiness, history, and backstory, it's well worth the trip.
So I'm afraid I can't recommend cutting out parts of it. That's why I remained silent after your first post.
Scarwall is awesome but there is a LOT of dead space in that place that can be trimmed. I think if you just read through it and found all of the places where the action was happening, you could condense it and save your players a couple sessions worth of game time exploring a whole bunch of nothing.
I'll ditto Jam412 in at least if you make them roll for traps on every door, and roll to search every room, it will be exceedingly tedious. I trusted them to roleplay 'properly', and only had them roll when there was something to find.
My friend printed out some 24" grid paper for me (5 squares per inch) and we had a pencil and straightedge and they mapped the whole thing out as they went through it. Gave the kids something to look at, they made lots of silly notes about the monsters they faced, and at the end we had a beautiful map of Scarwall. AND it let me say, "OK, you go through this set of rooms as carefully as you've gone through the others, so let me add those to the map and just point out the interesting stuff you find there..."
"Interesting stuff" was whatever I thought of that might keep them engaged. Scrawling on the wall. A ghostly bucket and scrub brush. Bloody footprints. Just random non-game-affecting haunts that kept the castle alive... er... undead.
Having just run my second session inside castle Scarwall, I can certainly understand the sentiment of Rockstream. Scarwall is becoming long and tedious, but that might be because my group has managed to avoid all spirit anchors thus far.
Jam412 and NobodysHome are right on. There's a lot of dead space that you don't need to detail out. I ended up just describing non-vital parts of the castle instead of drawing them on the battlemat. I also don't ask for search checks for every single door that leads to nothing, only when it's relevant. Wandering monsters and the skeletons that inhabit the barracks are out also. They are just time wasters.
So what should you keep? Whatever you think is awesome. I'm having a blast describing the place. Sial, and to a lesser extent, Laori make great tour guides as they describe the horrors that must have occurred in the castle courtyard, the historical significance of the Star Tower, and all the other rich backstory of Scarwall that the players would not otherwise know about without the two members of the Brotherhood of Bones.