Regarding your doubts, as has already been mentioned here, these books will be essentially fluff. In fact 80% of the material in these books will remain relevant in
SR4, because they are essentially setting books whose contents has been designed so that it's equally valid whether you are playing 206x, 205x or 2070. No doubt there will be changes, particularly to organizations and countries currently (206x) going through transitions but the vast majority of the material will remain consistent, up to date and relevant.
Much like most of the books since
DotSW these will also possess some tidbits that foreshadow
System Failure, but they are by no means essential, anymore than say
SOTA64 or
SoE were.
The main reason these are going ahead is to complete the picture of the Sixth World under SR3 (admittedly a
Shadows of Africa might've been nice but we can't have it all) and because their contents (with very few exceptions) will remain valid in 2070 as they are in 206x. They will also provide the most complete picture of the Sixth World to date
FanPro wanted to provide some development and in some cases closure to several current ongoing plots, before
SR4 kicks in, and in that regard
LA,
SoA and
SoLA do have a quite a few surprises. Before wrapping up SR3,
Loose Alliances (the sourcebook formerly known as Sixthworld.org) gets to detail many of the most important non-corporate and non-underworld players (and now that I think of it some of those too) in the Sixth World. Then
Shadows of Asia and
Shadows of Latin America in quick sucession, adding to the overall global picture and also building/wrapping/developing existing plotlines
As to their sell points, having read them, I believe that the contents of
Loose Alliances and the
Shadows of books will speak for themselves. The former is going to be almost as essential as
Corp Download and
Sprawl Survival Guide for certain aspects of the Sixth World and will not be replaced anytime in the foreseeable future. The latter fill in certain areas of the World (what you're not going to get the books where they finally cover Japan and Amazonia?

) and also continue to develop related metaplots (obvious ones include the PPG, Russia/Poland, Yakut, Japanese Emperor, Tibet, Lung/Ryumyo, Phillipines, Aztechnology, Yucatan and Amazonia...). While some may be recapped in future SR4 products, the vast majority
won't.
Will
SR4's announcement impact out-the-door sales of these books? Undoubtedly. FanPro might take a hit on these but at least its offering closure and an (almost) complete global overview for those player who are reluctant to move on to 2070 will have most of the world to play with. I 'm sure that beyond the hardcore collectors who buy everything (myself included) a lot of people will have doubts about what I'm saying, at least until
SR4 comes out. But I'm pretty sure Rob's counting on the fact that those reluctant to buy now will be picking them up later to get the whole picture...
Then there's also the issue of whether or not everybody who buys
SR4 jumps to the new ruleset and date immediately or will make the transition slowly in-game.
As I've mentioned elsewhere, we're also discussing the possibility that any setting rules included in these books (and the most recent ones) that aren't included in the new core rulebooks be updated to
SR4 via free web supplements on
Shadowrun homepage, which I think would solve any remaining issues with buying these books.