I really find this to be a non-issue. As Action Kamen says above this is a two sided issue, the first being posts getting tagged insufficiently, and the other being the "first" e-peen argument.
In my opinion the first issue would be real problem if it was what was happening. Insufficiently tagged posts have no handles to allow them to be retrieved via search, thus they are basically lost once they get buried (unless someone tries to upload that image again later and tags it). While not everything gets tagged to the thoroughness I'd like to see, it's rare that a post goes more than a day without someone adding the essentials. As you note, there are exceptions, and those posts should be gone through, tagged, and if there are trouble users among those posts, PM's or records given, otherwise I haven't seen it as a large problem lately.
The second issue of being "first" and establishing your e-peen is really irrelevant to the site's functionality (collecting and annotating good artwork, and making it available to others). I agree that it's frustrating to find a great post, see it's not yet in IQDB, and then that it was recently posted with few tags. But what was actually done wrong in that case, especially if the uploader is more thoroughly tagging it that very moment? If this happens to me, I simply tag and translate, vote, and move on.
Furthermore in many circumstances it is easier to do a better job tagging after the fact. For a series of images with slight changes, copy-pasting the common elements and going back later to tag the diverging details is easier and more efficient. For cases where the preview doesn't load or is missing from the upload page it's better to fill in the rough details from memory and then tag thoroughly when you can see the image.
If you are concerned about not being able to post good images at all, I'd suggest you look for less popular or older series, or for sources other than Pixiv. There is a ton of good stuff out there that has yet to be posted and is under no time-crunch to find. Even for Pixiv, the service you (DakuTree) provided makes it quite easy to find good Pixiv posts that have been passed over.
TL;DR:
Insufficient tagging is a real problem, but simply posting with few tags doesn't cause it.
Not being able to get "first" or enhance your own stats by posting new images can be frustrating, but doesn't adversely affect the site's functionality, and isn't a real problem that needs new policy to remedy.