Gnomes are described as coming from a place called the fey, which they refer to as the First World. It is said to be brighter, wilder, and more primal. Not only is it the home of the Gnomes but it seems to be a better place than Golarion. This begs the question: Why did the Gnomes leave?
There is a rumour - just a rumour mind you - that the Gnomes are flying from a really serious act of mischief that they did in the fey lands. And by mischief I mean accidentally triggering some kind of disaster.
The Advantage of Being Small
Gnomes are the second smallest race, and because of that they are, harder to hit (+1 to AC), harder to block (+1 to attack), and hard to detect (+4 to stealth). I think this more than makes up for the -2 to Strength.
Direct attacks are to be avoided for your Gnome PC - spying, recon, ambush attacks these are the territory owned by both the Gnome and Halfling races.
Spell Like Abilities
Gnomes get free spells that they can cast once per day:
- dancing lights
- ghost sound
- prestidigitation (small feats of magic; party tricks)
- speak with animals
This spell-like abilities seem to be directed at supporting that +4 Stealth bonus. You've got the makings of the ultimate sneak attacker in the Gnome.
Not Quite Here
When playing a Gnome it is worthwhile to note that the race is marked by being intrinsically foreign. And by foreign I mean really foreign - the Gnomes don't just come from another land they pretty much come from another dimension.
So if you'va always wanted to behave like a worry free mischief-maker here's your chance.
Some Gnomes have vivid natural hair colors, might as well go for that. Might as well dress your PC in a colorful garb too. Be a Gnome and enjoy it. And don't forget to shoot your mouth off to the other members of the party any chance you get - that too is Gnomish behavior.
And have your PC have some kind of weird personal project.
Reading about the Dwarven and Elven races I've come to the conclusion that, racially but not individually, they're simply not the adventuring types. Dwarves are too nationalistic, elves are too long-lived making them disinterested. Gnomes are the exact opposite. This race likes to wander and are extremely curious - they are the race that is most likely to go into adventures for the sake of adventure, not treasure or prestige.