I saw this topic on a thread at DF and I was motivated to say a little bit more about the general topic of how people "play" their non-human humanoids.
Where the MM might say that a race is primarily "Evil" or some other alignment, I tend to go in another direction.
As a matter of fact, I tend to view my non-human humanoids in a Star Trek lens.
For example, I see orcs very much like Klingons. A very aggressive and posturing race that pushes the concept of "honor" to extremes. Other humanoids that see themselves as "peaceful" have trouble understanding and getting along with them They also often make the sometimes dangerous and other times tragic mistake of assuming that members of this race are somehow "less" than their own.
Now, on the other hand, I see Dwarves as behaving somewhat like Ferengi. Very task and business/financially oriented. Short of stature with a big chip on their shoulder.
I lack the imagination, I guess, to do much more with Gnomes than to treat them as living versions of our garden statues. I don't have a Star Trek race that I compare them to. I see them as fun loving, few cares in life little rascals who LOVE to play practical jokes on others, not out of meanness or spite, but because they genuinely think it's funny. Especially when "Big People" are involved. If you are a "Big Person" and have a sense of humor, you can gain a lot of trust and friendship with Gnomes.
I think elves change as they age. They begin when they are young as more like Gnomes but as they age, they become more somber and serious, perhaps even a bit wistful as though inside they somehow mourn the loss of their youth.
While older Elves may become very Spock-like, they do not shun or look down on younger elves for their frivolity. Instead, they watch it go on about them while not actively participating themselves though no young Elf would ever dare turn their pranks and festiveness at older Elves.