I just read a book, "Why some ideas survive and others die: Made to Stick"
(by Chip Heah and Dan Heath). I was recommended it when I asked about
marketing and community building.
While reading it, I noticed that most of the perls of (marketing) widsom
also applied to game design.
One applied to my question about awarding XP points:
A pscyhology experiment was undertaken where people took a survey, and then
as per usual, were offered $5 for their troubles. However, the real
psychology experiment was that after being given $5, they had the
opportunity to donate some of it to charity. People were either given a
donation paper describing millions of homeless/hungry children in Africa, or
a donation paper describing a single child, Rokia, and about her plight.
Statistically, Rokia took in twice as much money as the abstract millions.
The phsychologists had a theory that thinking about statistics puts people
into a more analytical frame of mind, making them less likely to succumb to
an emotional appeal.
They ran a second study. In this, some people were asked analytical
questions, like "If an object travels at five feet per minute, then by your
calculations how many feet will it travel in 360 second?" Others were asked
emotional questions, such as "Please write down one word to drescribe how
you feel when you hear the word "baby"?"
Then, both groups were given the Rokia letter.
Those given the analytical questions before hand donated half as much!
Which implies, that a game showing numbers may blunt the emotional impact of
NPC actions and dialogue.
By the way, the book is worth the read, both for marketing, and if you look
at it from an odd angle, for content design.