There are some things in Me_'s post that I think should be commented on. I'll restrict comments to those things I can directly pick and implement from here. I don't design mechanics but I know those that do come here for inspiration as well.
Suggesting events, quests and decisions is mostly pointless too, as they never get added, although some suggestions resulted in Paradox adding their own events, etc. (e.g. for Tuscany or Orissa).
A matter of perspective I guess. There's no guarantee that a suggestions gets adopted wholesale but it can still serve to take the development in a certain direction. If I see a suggestions such as with Orissa (Tuscany was done during MN when I was away on parental leave though I did tip of my replacement about the posts about it in this forum) I'm not going to stick to the suggestion word by word but I may still be adding stuff I wouldn't have otherwise.
Those kind of suggestions are certainly worth my time but if you don't feel they're worth yours without a very faithful implementation then I guess you could avoid making them. You have some good contributions under your belt though.
Suggesting nations/provinces is mostly pointless as the map is pretty much full, with only Regensburg being Bavarian instead of a free city and Epirus being Ottoman instead of independent.
I disagree about this but I'm a map nerd and don't get the final call on when we add stuff to the map or not
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That's likely a good thing but I don't think future map improvements are entirely ruled out. I certainly have an area or two I'd like to do some changes to still. If I am told to expand the map again you can be sure I'll bring up any good suggestions I've seen, as I have in the past.
Suggesting formable nations is pretty much done as there are not many left to imagine. Yuan, maybe.
I imagine there are still a few that could be added, I tend to prioritize checking such threads out. Reforming ancient entity x is not something that speaks to me as I personally feel the game generally needs to look forward more than backwards right now (not direct at Yuan, it's just a general point that I feel should be made about formables).
Suggesting history files changes is pointless, as history files are no longer supported.
Later start dates are not balanced for when adding new features but if we're not fixing history bugs for later dates then nobody told me as I'm the one doing those fixes. Not sure where exactly this oft repeated statement originated but history files do get updated, both for bugs and when new features are added. They're just not tested the way the 1444 date is. Fixing bugs in later start dates is not a very high priority but it's something that does get fixed. There's a general tendency for players not to report history file problems just as there is a general tendency to not report event oddities which sometimes makes older bugs linger for a long while unless we happen upon them ourselves. This is understandable as fixes can take a while and probably also partly due to a legacy of odd effects in events and history going back to older games
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(and as the oddities *are* often pretty old most people are likely used to them).
Suggesting balance changes is pointless, as Paradox makes balance decisions by themselves.
What, how and when to implement as well as decisions on balance related to suggestions will always be up to those actually responsible for the game. That does not make suggestions, discussions or critique pointless. I guess this sums my point up pretty well. You may feel this means discussion isn't worthwhile but that's what these forums are for.
As for where the line goes between suggestions and general discussion, that's sometimes clear and sometimes a bit hard to tell. Asking for input or discussing something in general before coming here to make a suggestion can be fine IMO but this is the best place to have your suggestions actually read by us (I do tend to read general as well during my commute but I don't think one should count on all devs doing so all the time
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).