I love, love reading the "armchair dev" threads. No word of sarcasm, I usually find them genuinely enjoyable and like participating in them. I read/lurk on a few forums, with this one being the only one I post on because, in general, the people here understand more and I have more interesting conversations with them.
I've been in the industry for... 8 1/2 years now (fuck I'm old) and I have never once read a "game idea" that I hadn't heard before and was worth stealing. There are a couple of reasons for this, but it is mostly because there are lots of smart people in the industry and good high level ideas are everywhere. My experience has shown that we, and our ideas, are all a lot less special than we think they are. What really matters is the execution, and the hundreds of little detailed ideas that solve and smooth our the problems/operation of the big ideas. There are also other very good ideas that aren't feasible for technical/cost reasons, and other things like that.
Now, with that being said, reading player feedback about your game isridiculously importantif only because there are many more players than you and most of them probably play the game more than you do. On the other hand, you have to parse that feedback because it comes from a certain perspective, and with incomplete information. So player feedback is an important piece, but still only a piece, of examining your game.
When developers "steal" ideas, it is usually from already completed games, because you don't have just a nebulous idea but a detailed model to study to see how many little problems were solved.
I'm sorry, but every one of my ideas is 100% original and perfect. Tuco told me so.
That, and I can't believe that you've never seen a good idea on the internets. Either devs are lazy in general, or can't think out of the box in how to solve issues. I suppose this line of thinking leads us to DIKU-derivative-hotbar-questfuck-treadmill games over and over again.
I dare someone to make a game that doesn't follow the pattern of:
Log in for firs time
Make character, pick class.
Find first quest, heart, xp area
Repeat process of quests, events, fates, hearts, whatever in a boring grind.
Do dungeons.
Hit max level in 40-100 hours.
Do versions the same dungeons over again, but now the mobs hit a little harder.
Do dailys, battlegrounds for points or tokens and save to buy something.
Do raids once or twice a week for 2-8 months before you do another on.
No MMO has launched that has broken this paradigm and was actually worth purchasing.
AOC - Interesting combat (but ultimately shitty), broken game.
TERA - Best combat ever, boring quest grind with nothing at the end of it.
TSW - Good leveling experience, interest class system, ultimately the same hotbar combat quest grind game with heroic dungeons.
Rift - WOW clone, was fun for a while as something different. Development made it stale after they couldn't properly create or balance classes worth a shit and couldn't properly utilize their Rift tech.
FFXIV - It's a classic game, that's just boring. Fun for a time because it's a decent classic style game, but ultimately (imo) just boring. I won't play a game with a 2.5 GCD and hotbars.
GW2 - Great combat, static boring world. Terrible class development, beautifully crafted world that is ultimately not very dynamic. The combination of hearts, events, achievments and map completion was the 2nd step in an evolutionary process that started with WAR's public quests. We're still waiting for evolution though.
WAR - Shitty game, shitty engine, shitty design. Fun PVP until you got to level 20. Will always be thanked for Public Quests.
What else?