I'm a ftp and I don't plunder (on principle, I could easily do it)
My income since the end of the last lucky board(when I am broke, or at least close to) event is around 2700(spent 800 on rune key mystery fruit, had 1900 this morning, 1800 of which went to lucky board). End of last lucky board would be 8th of june, so 21 days ago.
600 of that is from convoy which conflicts with the plunder bit, so my "other" income is around 2100 in 21 days, so around 3000 a month.
Now, I might have some calculation error in there (or remembered something wrong), but it's definitely over 2000 a month, considering just fox, group summon and group wheel gets over 1500, close to 2000 a month for me.
Your estimate of 1000 seems like a gross underestimate.
Not that 1k extra coupon in "others" really change things much, your overall point is valid. I have more or less given up on rank 7 armor. The cost as it stands now is ridiculous. Unless adv thread became available elsewhere, such as monthly or lucky board, I'm not going to bother.
Personally, i feel they should replace medium thread with adv thread on hard SA, that would be a good start.
As far as space-time shop goes, the current credit:coupon value of adv thread is already one of the best buy, only second to the tactic box which have its problem in being forcefully diversified. So I really can't see a huge reduction happening there. I would love it if the exchange shop have adv thread available and takes low/med thread as well as all forms of cloth in for trade thou. Even if the trade rate is horrible, my hundreds of all 5 of those time, over 1k in case of low cloth, should be able to get me a few dozen adv thread at least.