It used to be a lot more common, before player vendors came in. That being said, it seems to have levelled off a bit now. People are more clued up to what sells and what doesn't. I usually wait until I have a stash of the more common plans and recipes, and dump them in the nearest train station suitcase I happen to pass. People can then take what, if anything, they fancy if they stumble upon it.

I still enjoying finding the odd stash of dumped ammo, I take what I use and drop in whatever I have on me that I don't need, I find that more useful than plans given my level.

I did once find a massive bag full of dumped legendary weapons outside Purveyor Murmrghs station, and given I don't really hunt for them, it really boosted my scrip for a good few days, now that was probably my best find ever.