I like the way you're thinking, though I think I disagree on many of the specifics.
1) Seems like a lot of what you (and many others) have suggested for dead planets are either covered by asteroids or starbases. I personally like the useless planets. For me it helps the feel of the game because it makes the habitable planets seem that much more special when you find them. That being said, I think that some dead planets will be incorporated into the strategic resource system they will be introducing. I understand that most other people don't like having those useless tiles, but I think that it is important that if they do decide to make them usable, they add something to the game and aren't just redundant of other mechanics already in the game.
2) Really like this idea and pretty sure they have already said that races will have different tech trees.
3) By divergent paths do you mean multiple ways to get the same tech? If so I like the idea, though Stardock has traditionally had very linear tech trees, allowing you to deeply specialize if you want. This is one of those areas where I think that there is a balance that needs to be struck between making the tech tree seem a little more interesting and keeping the feel of GalCiv. As to certain techs triggering events, the basically said in the stream on Friday that they are interested in that type of thing, but it will depend on how much time they end up having to create events. On the bright side, they also said that events will be moddable so players can create and share their own, and based on the way they've handled FE DLC, I would guess that and Events pack would be a very likely release.
4) Weapon specialization sounds very interesting and could be very cool.
5) Remember that at some point you won't start off at war with everyone else, which will help the safety of your survey ship. I also like the balance with the survey that you want it to explore, but if you over extend there are consequences. That being said, I do like the idea of salvage. Every combat could leave some behind, and special salvage ships could collect resources, credits, and maybe even foreign tech.
6) While I do think that invasions should be a little more interesting that in GalCiv II, I don't think full-scale tactical combat a-la FE or Total War or something is a good fit for this game. Invasions still need to be fast and largely based on tech and numbers rather than player skill in order to keep the focus on the larger galaxy-wide game.