We don't really set the spawn rate, we actually set a minimum and maximum for population values and the server does it's best to keep up dependent on load.Perhaps @Mesanna or @Kyronix can explain why some of the camps are on extremely short (10s-15s) respawn timers. There's absolutely no reason it should be that short. For example the balrons, evil mages (spawn 2 at a time), oozes/snow elementals (spawn a pair at a time), liches, golden elementals, etc practically every camp has instant respawn after they're agro'd/killed. You're just asking for this to be scripted/cheated.
I scouted a few servers the other day and in Trammel alone there were 22 people, mostly sampires, camping 1-4 per in the camps listed above. All 100% afk.
Also, as an aside since it's been brought up in a thread, If you feel someone is breaking the ToS with regard to Blackthorns, feel free to page a GM. Of course, the results of any action the GMs take, as well as any future anti-afk changes we make we can't comment on.