Is there a mod that just improves mercantile and speechcraft of all traders? It should not do much more than that.

HotFusion's Economy Adjuster's Merchant Skills plugin is what you'd want. I use http://btb2.free.fr/morrowind.html, and it works fine.

Thank you. I remember HotFusion's mods, don't recall what made me uninstall them years ago. I will try BTB's version.

I haven't run the economy adjuster because it sounds a bit annoying to have this disruptive event every time you talk to a merchant a first time. Instead of a script (which will only work on new save games) wouldn't it be better to adjust them individually in the CS? That would also work with existing saves.

It extends to more than just merchants. I know it affects caravaners and shipwrights too, which plays a little havoc with mods like the Pearl Palace which rely on a greeting to trigger the mod content. I'd switch back to PirateLord's economy plugin but I'm a little intimidated by trying to make that work properly in an object merge.

I think this was the root cause for me disabling HF's Adjuster. Today I do not use 300+ mods anymore, but nevertheless...

Maybe something like only the NPC changes by PTE.

According to the readme, the main point of contention in including it in an object merge is that the adjusted inventories can cause crashing, and that the affected NPCs need to be removed from the merged objects plugin for it not to crash. I looked at that and thought "But wouldn't that also remove any other changes to the NPC from the merge?". I think including just the Speechcraft/Mercantile adjustments would work, but I'm not proficient enough in the CS to just isolate those. It took me forever to figure out a workaround to the Pearl Palace thing.

Well, you have 3 options.

Don't remove the NPCs, and gamble on the game not crashing
Remove all NPCs in merged objects
Identify the NPCs that PTE changes, and only remove those from merged objects (Slooooow process).

It all depends on what combination of mods you are using. Mods really shouldn't be adding/removing items to vendors (like new weapons or armour), but put in new containers that are owned by the NPC. Much safer and less conflicts.

I think I have found a working solution with (mostly) PTE now, thank PirateLord and Enchanted Editor.

Thanks all!

By what you're saying, it sounds like the mod would only affect the inventories as opposed to the NPCs themselves (and that the speechcraft/mercantile changes wouldn't conflict). Correct me if I'm wrong, but would it be safe to run PTE outside a merge with several mods (BTB's mods, LGNPC, Light The Way) that would just affect the NPCs and not touch the inventory?

BTB settings.esp has a few conflicting NPC entries (18), e.g. Arrille and J'Rasha with direct inventory changes. So, there seem to be always some NPCs either get overridden or you have to take care about.

D'oh, the soul gem vendor changes. If I were to delete those with Enchanted Editor, would they play nicely together after?

EDIT: Looking at the mods with TESPCD, it would likely be too complicated to get everything to work together without problems, so that idea's out the window.