While I agree with you that the content of the last few releases have been fascinating but mostly inconsequential. The reason given for staggering the releases is a good one: if you released it all at the same time, each individual issue would not get as much attention. Assange also states that Wikileaks makes a promise (among other promises such as to protect their identity) to its informants to try to achieve the maximum possible impact on the world due to their leak.
It could also be a way to spread the ideology of leaking information. I'm sure there is more than just a strategy to leak the information they have, but to add momentum to the whole idea. Undertaking such a controversial objective could be backed up by a belief. It seems giving the sensitive nature one would assume there are larger objectives involved than the attention created, or it could be as simple as that.
I also see it as following the motion picture marketing model. Build interest months before the release, develop buzz, and then increase that to a countdown ramp-up.
Seems to work quite well, and indeed you are correct it does keep individual issues from getting lost in the release process quite well.
Building hype and waiting and releasing information in parts also dilutes the Wikileaks brand as a publisher of important information, so there is a trade-off involved.
