Game development is an iterative process, and while this does grant you a good amount of freedom to experiment with new ideas. How much time you devote to each iteration is extremely important since each one inevitably costs you development time, so separating ideas that work from ones that don't quickly becomes paramount. Obviously you won't always know that what you're attempting is in fact a poor decision until you test it out, and there's no shame in that; sometimes things simply aren't as fun as you imagined they would be. More importantly just because the concept is bad in the current game you're working on doesn't always mean its a bad idea in general so you can keep it around until you find a better place for it later. Where there is a serious issue though, is when you've convinced yourself certain aspects of the game must work no matter what. What is important isn't whether or not you personally like the concept, but rather: 1. Whether the concept works in the first place. 2. Does it play well with the game thematically and in tone. 3. Finally whether other people agree that the mechanic is fun within the scope of the game. The final one is one of the parts that can get you into trouble, because to often people will hear feedback along the lines of "Well this thing is fun, but it doesn't feel like it fits." From that feedback the instinct might be to make sure it gets into the game period because you were told its "fun" but even then you may only end up muddying the game.
As a quick aside, these games ARE NOT associated with UAT at all. I want to clear that up right away just to avoid any possible confusion. With that being said, this was a really cool project that I stumbled upon recently. It's called Final Fantasy VII Re-imagined. To me it's not only a cool concept but an amazing design exercise you could practice on your own. What if your favorite game was a different style of game entirely. We're not talking "Turn a FPS into a TPS", but instead an RPG into a beat-em-up like has been done with Final Fantasy VII. The game is just a demo but you can download it for free and give it a shot. It's really interesting to see how they translated everything over and kept the game as intuitive and smooth as they could. For instance, the materia system still exists and it's been incorporated into the combos as you make your way thorugh the game. There's something really satisfying about finishing a combo and having lightning smite your enemy on the final blow. You can download the demo here: Final Fantasy Re-Imagined