We seem to have focus on a cross-platform installer, but I wonder if it's better to use native tools for the job as there's a lot of pre-existing frameworks out there for creating native installers. Whereas I believe the cross-platform installer that Goober is working on is more of a build it from scratch and replicate the install guide kinda approach.
I'd say the advantages of having a cross-platform installer are the same as those for having a cross-platform launcher: a single codebase to maintain and develop, coding prerequisites being just a single set of skills (in this case, Java and Swing) rather than skills for the tools specific to each platform, and simplified tech support because of a consistent codebase and UI/UX across all platforms.
Diaspora released a Windows installer and an OSX dmg instead of a cross-platform installer. (of course they have the advantage of no retail data... and Linux was left out - but seriously given the fragmentation of Linux distro's I don't blame them!)
FWIW, the main reason Linux was left out was that no one on the team had the expertise needed to maintain native binary packages (deb, rpm, etc). I was really hoping that people in the various distro communities would create binary packages for their distro, since I thought that at least some communities did for BtRL (although I can't find any links to support that atm), but I guess that was wishful thinking.
EDIT: As for whether we'll shrink and die without an installer, not sure. It seems like many people are able and willing to install at least FSO itself manually, but for installing mods, there's probably been a big decrease, since that's quite a bit more complex. If the pool of people playing new and previously unplayed campaigns is drying up -- and it could be -- then yes, that would spell serious trouble for the community IMO.
EDIT 2: I will concede that using the tools for building native offline installers (at least on Windows) is much
easier than rolling our own online installer, although I don't know how easy it is to build installers on the other platforms. The difficulty of making the new installer depends a lot on how close it is to being done, though.