Howdy. Getting to the OP's question, I believe that we really cannot see the true effects of our LI's and influence until we actually play the game. Certainly, there are livestreams and other videos, but I presume they are only of the early to mid portion of the game. Suppose, then, that they assist with the latter portion?
And in regards to them returning in ME3, it seems -highly- likely. Bioware has stated that continuity will be a large factor in the Mass Effect series, and to ignore such a thing would be alienating to some of it's largest fans (Of which, it can safely be assumed, most people on this forum are, to one degree or another).
Now, I am not saying your point is invalid, Mr. Littledog, but I am simply of the cautiously optimistic side of things. No doubt we will have this conversation in five days time, or so, and I'm sure we'll all be better informed on the exact situation involved.
Though, there is one more point I wish to raise. This is strictly my opinion, and not meant to denigrate any others located in this thread or the forums therein... but I found the ME1 LI's, compelling, but also... very slow, so to speak. The characters had little room to grow, I believe, especially in the case of Kaidan, who pretty much underwent all his character growth prior to ME. So, as an alternate theory, suppose the reason they're excluded from ME2 as squadmates, is due to the fact that over the time that we're dealing with the collectors, those characters can grow and mature into something different? Experience more character growth? Just my two credits, so to speak.