I'm going to assume we have collective forum amnesia or people just didn't see the thread, but not so long ago there was a similar thread on here and this image popped up. It shows the probability that you will know a random word (y axis) versus number of words you know already (x axis), assuming you learn the words in the order of highest frequency->lowest.
So as you can see, it has a number of curves. The top two are word lists which contain 15,000 and 60,000 with no proper nouns, and the "cb's innocent novel frequency list" contains 300,000 words with proper nouns included.
90% coverage is a pretty good benchmark for I'd say the minimum knowledge required to actually enjoy reading. For the smaller lists, it occurs at just under 5,000 words, and for the big list, it occurs somewhere near 12,000 words.
The novel list will obviously be biased towards more rare and poetic words, and the smaller lists might be more restrictive, so you can take it with a grain of salt, but it gives you an idea for how many words you need.
However, I'd stress the
minimum part when we talk about the numbers above. You probably want more than 90% coverage. That tends to mean at least 1 unknown word per sentence, which is a bit of a bumpy ride.
Personally, I did core6k + all the (P) words in edict - all the katakana words after core6k. I also deleted all words that I considered obvious (it happens-- after you've done 6k, you get a sense for things). That landed me at 13k approximately.
I agree that studying katakana words for recognition is pointless 90% of the time. Its pretty easy to recognize the english word they are going for. What you really need is production-style katakana cards so you can actually remember which words you can import from your existing vocab, and which you can't.
But anyways, I thought at first that this would give me like 99% coverage or something, but now I realize that I'm still not there yet. Core6k and the (P) tag are both based on primarily newspapers/academic sources, so they tend to leave some gaps lying around.
Thus, I'm still adding to anki. I don't think I'll ever stop in the near future. I have no problem with the whole attitude of "add everything you don't know". If it came up once, maybe it will come up again, maybe not. A single card in anki takes up so little time to add with rikaisama, and then over its lifetime, you get like 20 reps at 5 seconds each, its like 1.5 minutes of your life in total. You could easily make that up later, when you spend less time puzzling over trying to glean the meaning from context. Also, I've talked before about what I see as a bit of a snowball effect when you start getting an intuitive sense for the kanji.. one vocab allows you to make connections to multiple others, making it easy to pick up more and guess at meanings, etc. Its a hidden benefit of adding lots of vocab that makes the deal just a little sweeter..
I do see what dtcamero is saying though, because after you've been through so many cards, you become so naturalized to the process that at some point you gotta make an effort to break the routine and move on to more practical study. Still, I don't think we need to shame people over using anki a lot. The average learner doesn't come into the language learning scene super hyped up to learn 10,000 vocab, but that's pretty much what it takes... so why not just tell em "shoot for the stars"...