I think this topic established the nature of the tagme tag quite well: This tag should is well used on posts that are tagged on an mediocre level and if you can't remember/find tags or don't know them.
This tag isn't to be used when there is a lack of the most basic tags (That covers tags on the lowest level on howto:tag_checklist.
Anyway, I go with the first option that you have provided: Tag it "something". Then adding tagme is valid because there are some tags you can find the post with.
Number 2 is a pretty shitty option, but it seems that we don't have time to look over everything. If an user excels at number 2, then a neutral feedback should be written (or a Dmail), leading them to howto:tag and the aformentioned checklist wiki.
But if you added tagme then you definitely looked at an image and I truly think that even more tags can be added in the same process since you are already in Edit mode. I guess that shouldn't really apply to lurkers, but to users who definitely know some tags.
I think it's asking too much to pointedly search for these posts but if someone happens to cross over such a post, then it should be in their interest to find to tag with a normal amount of tags as soon as possible and not hoping for someone who cleans up tagme.
At least, there are some basic tags to start searching with, even if you add tagme and it reduces the odds of not finding a post as soon as possible. The most tags can always be added afterwards by someone who looks though tagme.
The problem of bad tagging gets resolved with something else, though. There you can add/remove tagme so many times you want to. It won't change the uploader's habits. But that's when the feedback system comes into place or contact them via a mail.