For those on MacOS or Linux, you can use Legends Browser which is coming along very nicely too. Most of the suggestions in the OP's list are either implemented in Legends Viewer and Legends Browser, or would be fairly simple to implement. One slight annoyance is that some of the information requires DFHack to get out and often the data is inconsistent. Toady has said that the XML dump will export more info in the next release, but I'm not sure what will be included. I'm very hopeful, though.
I do agree that legends mode is missing a bit of information, though. One thing that bugs me quite a bit is that adventure mode does not really interact well with legends mode. In other words, things that happen in world activation are really hard to recognise in adventure mode. For example, I noticed that in a dwarven town the militia commander and the sheriff were goblins. Not only that, but they were beating the crap out of everyone. I killed them. Afterwards I looked in legends mode. What I saw was that there was an insurrection attempt and the the attempt failed because the participants disappeared. There is no indication of whether or not what I saw was the insurrection and if I had actually killed them.
Similarly, I can see from rumours that an army is on the march. I can kill that army and when I check legends mode, I see nothing. I'm guessing because the army never gets to the destination, it never registers as a battle. One time, I was in a dwarven fortress and suddenly a whole bunch of attackers from the nearby dark pit arrived. There was a huge battle (in which I killed 25 of the 40 or so that showed up). Absolutely nothing in legends mode (apart from the usual "so and so was cut down by so and so". No idea why these guys were there, whether it was a battle or not, etc. There wasn't even a war happening between the two civs, so it's just bizarre.
Really, it seems to me that anything that can be recorded by world activation in legends mode, should also be recorded by adventure mode. Otherwise there isn't much point to adventure mode (in the grand scheme). Even the simple "Adventurer Joe visits Monkeyforge" is missing.
Possibly that's not completely related to the OP's suggestion, but in terms of "better description of events" I think it will help a lot. It means that if you look at recent events in legends mode, you can jump into the world and see things unfold first hand. If you don't understand what's going on, you can back out and look in legends mode.
But like Shonai_Dweller, I don't want *too* much information because some of the magic might be lost. I once had a companion that had been kidnapped in a dark pit. After many years, he managed to escape back to a dwarven hillock, where he became a ranger. All the rest of his family had also been kidnapped, but none of them had managed to escape. We were wandering the countryside, where we were attacked by a group from the dark pit where he had been kidnapped. Suddenly he changed sides and attacked my other companion. He went from being a companion to having "Lethal" status. I told him to cease fighting, but he refused. I had no choice but to kill him.
Looking at legends mode, it seems that the group that attacked us included some of the dwarfs he had been kidnapped with. I could not think of another reason for him to suddenly attack. Legends mode only says, "Agreement was terminated after a violent dispute". Now there is no doubt in my mind that he, being conflicted about fighting his old comrades with whom he suffered together for years or fighting his new companions with whom he'd been together for only a few days, snapped and chose his old ways. I'm also pretty damn sure there is no code in the game to do that ;-) It's just one of those magical, things that "happen" in the game *because* there is a lack of explanation. (Although, Toady does often hint that there are goblin spies currently in the game, so that could bit it as well...)