posting my opinion on the general decreasing interest in participation..
regarding the placement:while it may be discouraging and/or intimidating for one to have your score beaten by a lot of people, think of it as an opportunity to test, measure your current skill level, against yourself. Either try to find where your current "wall" is, or try to overcome your current limitations to see where your current abilities can take you to, if you use them to your current best potential... it's up to you.
Then, when you look back to the challenge, later, after having played more shmups and had acquired more experience and have more abilities to transfer to the game, watch how you've progressed! Don't push yourself for improvements too hard, though, progress rhythm isn't something that's entirely controllable. Play against yourself, primarily.
Remember: the people who can score high don't laugh at those who can't; they've learned to respect the effort and perseverance of other players, like themselves. (personally, shmups forum's annual STG Tournaments are a rare opportunity for me to appreciate a lot of people trying to do their best, and that's a very.. beautiful thing to behold and take part of)
regarding scoreplay:for people who're not used to playing for score, doing so may sound as loading yourself with additional work, making survival more difficult. For some, it may also feel more restricting (for example, if you trade bombs or even lives for a better score, or have to risk yourself more). For said people, when looking at higher scores on the highscore tables, they may feel demotivated.
My words, regarding this feeling, is: don't treat the bi-weekly tournaments as your last, or only chance to try to test yourself or compete against others. The games weren't made to be enjoyed specifically for bi-weekly tournaments such as these, so you still have a lot of opportunities to revisit said games, as long as you like them, in your own pace. Maybe you'll even get to appreciate the game more, at a point where memorization becomes less of a problem, and thus you'll be motivated again

regarding the bi-weekly tournaments themselves:
please keep them going, Sapz, you (and whoever's helping you) have been doing an awesome work, and I'm very grateful, even if I skip some weeks.
Some people here have said that they enjoy survival more, let's hear from other people what characteristics they also enjoy!
Ideas for the next TH Special tournament:
UFO base point value ranking? (besides grazing, this would require people to get UFO tokens while an UFO is active, maybe rainbow UFOs for more UFOs, instead of blue/red UFOs)
TD no bombs (but Hypers on)?