That matches my experience. In New Game + you can come out of Part 1 with two magical items you could not obtain before (jeweled medallion and ring of green metal), and a third (black skullcap) is available much earlier in the game. With the ring of green metal, you can access a new encounter in Part 2 which gives you the clue for the new encounter in Part 3. I also did not find anything significantly different in Part 4.
Just for fun, I came up with an "ideal" playthrough that allows you to experience most of the different options in parts 1-3. Part 4 still has too many potential endings to explore them all, but that's where the game-ending rewind comes in handy. S1: Visit Daddu-Ley S2: Learn Moulas' spell line through Sirisi/Temple of Slaang and Theetah's spell line/order through sewer encounters S3: Use the beacons, meet Aliizi, worship Y'Bran* S4: Rescue Aliizi S1+: Visit Cantopani S2+: Learn Moulas' spell line through note/corpse and Theetah's spell line/order from Courga S3+: Avoid the beacons S4+: Avoid Throben's curse *Having Y'Bran gives you more flexibility in S4 to Spoiler avoid killing Jann and lift Throben's curse more easily but you can still Spoiler get rid of him at the shrine in the fields if you want maximum stamina, and/or remove Throben's curse with the hourglass if you want the Cartoum ending
