The difference between the player and the designer is just that the designer has put time into thinking about design, and with that time has probably acquired a broader experience and more developed conceptual framework of what a game is and how it functions. With that experience and theoretical foundation the designer has mental tools to test ideas (and how they fit with other ideas) that an ordinary player doesn't have, and the designer also has the habit and mental toolbox to produce more ideas faster.

Very well said.

Every designer has to _be_ a player, just like every writer has to be a reader, every musician has to be a music fan, etc. If you're not consuming it you could make random attempts at producing it but you're not going to have any feel for what's functional and enjoyable.

One possible counter-example to consider would be Shigeru Miyamoto. Despite arguably being the world's most famous and successful game designer, he reportedly spends very little of his time playing games. I'm sure he plays the games he's working on, so your argument may still hold in that regard, though it would seem that one can still theoretically be an incredibly successful designer without actually gaming regularly.

(But don't get me wrong: I'd certainly agree that playing others' games would have a much greater benefit to a designer than not doing so.)

However, players/gamers can sometimes come up with amazingly detailed explanations of why certain features should stay/go. E.g. I found enlightening analysis done by fans about bloom and armor ability in Halo Reach (its not as straight forward as "bloom and armor ability is good/bad").

Good point, there's definitely pros and cons with both groups (gamers and developers).

However, I would like to emphasize that I am not trying to intentionally add in "unenjoyable" activities. The goal is to somehow make it fun to repeat old content.

I think the most ingenius example of a positive grind in gaming history must be Diablo's system of difficulty (normal/nightmare/hell; where you need to beat the game in a certain difficulty to get the next unlocked). Essentially the same content all over again, yet wrapped around a context that makes sense and it's incredibly fun.

I'd be curious to see whether psychologists have studied, and given a name to, this particular phenomenon: the disparity between what individuals think they want and what they actually want. The phenomenon is certainly not unique to just games.

This topic has been extensively studied in economics. E.g. http://en.wikipedia.org/wiki/Revealed_preference

Basically it says that asking individuals what they want is useless, and the best way to find out what they want is to actually see what they end up picking.

"Preference" is a huge topic in economics, both historically and in current times. It is highly mathematical and rife with controversy and debate (see Rational Agent Theory, Expected Utility Hypothesis, Behavioral Economics etc).