If you essentially want to hear the master tapes, the Futureland releases are the way to go. Toho Music Corporation's sound quality for the Perfect Collection is so-so, but some of the stuff found within those six boxes is the the only way you can hear a specific Godzilla score in complete form, like Michiru Oshima's score to "Godzilla vs. Megaguirus" for example. Also, some of the score representations found elsewhere with the boxes are haphazard at best, but that's only limited with the Heisei material outside of the scores to "Godzilla" (1984) and "Godzilla vs.Biollante" if memory serves me correct. Of course, the source used for the second disc of Biollante will cause one to question what Toho Music Corporation was thinking.
As for getting all of the scores released here in the U.S., just the licensing alone will be costly. Even in Japan, music licensing from Toho and other film studios is costly, which makes CD releases there expensive. I have a friend who runs a Japanese label (Cinema-kan), so I know what I'm talking about. Since we're talking about Godzilla here, the licensing to release those scores here will certainly be costly and Toho would probably be demanding in terms on how they are released. LLL was lucky when they pulled off their two releases, and the old Futureland releases are still better.
If they were to be released here, and given proper representations of each score as well as proper package design, you may talk about each score being between $30 or $40 each, maybe even more for some. Pricing would most likely be a factor on how costly it would be to obtain the licensing for the scores.
Long story short, while it wouldn't be impossible for all 29 Japanese Godzilla scores to be released here, it would most likely be an incredibly costly process to fulfill, and may not be worth it if the demand isn't high. Even all six boxes of Toho Music Corporation's Perfect Collection are sitting at their warehouse collecting dust. In fact, poor sales were a factor on why it took them several years to get all six boxes released.