Nice. Here's a few suggestions for generic story screen art:
1. A post-battle view that could be used in more situations. Basically just like your latest one, but with nothing that clearly shows who fought there: it can have arrows, spears, a flag, maybe a loose helmet somewhere and so on, but no human/elf/dwarf/orc bodies lying around. Of course you could have some in the distance so they're not identifiable (beyond perhaps being identifiably humanoid).
2. Sailing. An image showing a ship or ship,s but not the specifics them or their passengers. Could be used when there's some sailing involved, regardless of who is doing the sailing or for what reason.
3. Cave scenes of some kind? An interior of a cave, entering a cave (probably the image would show a mouth of a cave) and finally seeing some daylight again after a dungeon crawl.
Forgive me for the following off-topicness, I feel like describing what I've been thinking about sometimes:
Personally, I'd rather like the following model for story screens: a story screen for the major points of a campaign, no more. In HttT for example, the major points are IMO Siege of Elensefar / Crossroads, Dwarven Doors / Plunging into the Darkness, Scepter of Fire, and Elven Council / Return to Wesnoth. The same story screen image could well be used for every scenario of one "section" of the campaign, if it's generic enough. For instance, the first section (scenarios 2-6) could show a rag-tag band of rebels marching along the side of a forest, with some coast visible in the background. For UtBS, one could simply have the story screens depict someone writing a chronicle (Kaleh of course; but it'd be silly to show his face there IMO), since the story screens actually are excerpts of his chronicles, as stated in the beginning. Of course it'd be nice to have a few different images of that (the first one with a little bit of writing, a second one with some complete pages lying around, a third one with even more, etc), but you could keep the same simple theme throughout the entire campaign and get away with 3-4 images without it looking cheap or like there's anything missing.
Think of something like the original Warcraft: at the beginning of every mission, the briefing screen showed the same image (if playing humans, it was some mage and a commander with a pint looking at some maps on the table, if orcs, it was something else), yet it didn't really look silly or repetitive because you weren't expecting it to be a realistic illustration of what the guys would in reality be doing right now (contrary to what most of our story art seems to try to do). IMO the same style could well work for Wesnoth campaigns as well, except that we'd use several different images as the campaign progresses.
Of course it might not suit all campaigns: in fact I think HttT was a poor example (unlike UtBS, which I think was the best example I can think of). But for some campaigns, I'd much prefer something along those lines than having HttT-style story screens here and there, and using blank (or only the bigmap) elsewhere.