Hello, it's Paulo again!
Now to talk about general design principles.
One thing every aspiring game designer should have in mind is that everything MUST BE DONE ON PURPOSE. You just do not throw game elements around because they're cool. Dissonant elements do the charming trick of not only taking the player out of the game, but of making them stop playing the game, and, in some extreme cases, making them return the game to the shop claiming a defect and making them trade your game for the first thing they see on the shelf.
In short, not good.
That does not mean you don't add new elements because they're cool ---- you make sure they have a purpose within the game. Even for old elements - if your team points out one element does not fit, you have to swallow your pride and seriously consider taking it off - but make sure they can point out WHY it doesn't fit.
This is valid for all sorts of games, even shooters, racing games, sports games - the more solid and purposeful the initial framework is, the less likely it will have to be completely torn down and rebuilt from scratch several times, and the more likely any proposed changes will purely refine it further, and even that eventual correction and retifications (known as RetCon for short) of the plot in later games will blend in more smoothly.
For instance, the whole question of Trap Books in Myst is a massive RetCon. Why? Because the Miller brothers simply didn't think Myst would be enough of a success to warrant a sequel, let alone a complete fictional universe. When it did go well, they had to do quite a few RetCons... however, the original Myst was well-built enough to withstand the necessary RetCons, which further demonstrate the point. If the millers weren't skilled, Myst wouldn't be such a success, nor be so easily inserted into a larger universe.
The point is: If you say to yourself or your teammates "well, put whatever we have in there" or "ah, just insert in some filler", or "pick it randomly", or "I saw a cool thing in another game, put it in whenever you like" too often, and, worse, don't check the result or test it..... well, your game is probably done for, unless your team is very skilled.
Bad producers kill good games. Bad designers, animators or musicians can wound a game. But bad producers are always the ones who deliver the final blow.