On all things HiE related:
I think the electronic drums were only used on the singles, as I've noticed a difference between the three singles (Cover My Eyes, No One Can, Dry Land) and the rest of the album in terms of the drum sound. Everything else was Ian's acoustic kit.
Speaking of the desire for hit singles, I know H likes to play it off like it's not a big deal, but I really do think he wanted a greater degree of fame than he got. Maybe it's me, but I've always sensed a hint of envy in songs like Deserve, 3-Minute Boy, etc, or even in interviews where he mentions people like Sting. He tries to play it off, but there's always a little bit of jealousy in his musings on fame.
I was so used to the American track listing that hearing the remaster with the original order threw me off for a long time. I ended up making a playlist from the late 90's remaster series that had the US running order. I like the flow with Cover My Eyes and No One Can kicking off the album and then the drastic feel change with Splintering Heart. Feels kinda similar to the feel change from Jigsaw into Emerald Lies on Fugazi.
Stads mentioned Tony Banks, and I think Steve Rothery is very much the Tony Banks of Marillion, as in, the band doesn't do what Steve doesn't want to do.
As far as Mark being the main prog guy in the band, I think that was most evident in the live versions of the This Town trilogy. They usually stretched out The Rakes Progress live (they did when I saw them on the TourFund tour), and that's when Mark got to get in some of the more "widdly bits" as he calls them. Otherwise, he's pretty low key on HiE. Hogarth, I think he's into the proggy, experimental stuff as well, but I think he comes from a different approach than Mark. I think that's why he and Richard Barbieri work well together outside of the band.
Beyond that, I love the parallels between the 4 Fish albums and the first 4 Hogarth albums.
Script and Seasons: First album for each singer. Lots of material written prior to member(s) joining. A few 8 minute epics.
Fugazi and Holidays: Difficult second album, kinda short on material for both, pressure to live up to the prior album.
Misplaced and Brave: Concept albums with children as part of the theme. Band is unified in terms of the direction.
Clutching and AOS: Thematically linked albums concerned mainly with the darker side of fame. Big changes lurking around the corner for the band.