For those joining the hunt, I'll post it again:
Okay, the following makes it a lot quicker to mark the threads:
Create a bookmarklet, i.e. MarkAsSpam, in your bookmarks bar.
Instead of an URL enter the following:
javascript:(function(){$('.r_t_p_no_EN').show().click();$('#markSpam_1').click();})()
Open each spam thread (i.e. ctrl-click) and then go through the tabs hitting the bookmarklet each time. and CTRL-W to close the tab.
Tested in Chrome and Firefox. FF works better since you can close the tabs even with the Thank-You-alert-box open.
With this method you not only save clicks (only one instead of two), you also skip the "bury thread" animation, since the script can click the "report" link even if it is not yet visible. Also the Bookmarklet is a lot easier to hit than the small (-) button.