The fact that you have to pay off speedy messengers implies that speedy messenger harassment is not only allowed, but intentional, and that bribing the speedy messenger service is speedy messenger harassment counterplay.
The meta solution is to riot about it on the forums and dismantle the speedy messenger system. I don't really have a horse in this race, though. People getting random speedies in the middle of important meetings about how their staff is ready, or embarrassing love notes is peak Arelith.
Aesthetically though, a near omniscient organization of halflings that can hunt you down within seconds of a message request -- including hunting people down on Skal -- is terrifying. But accurate. As we all know, halflings are the outer-evil we've all been warned about, and once their dark tapestry of madness is complete, they will drop their guise as pie-coded hedonists and plunge all of Toril into a languishing, wasting despair. Decay of the flesh. Decay of the mind. Decay of the spirit. The gods will prostrate themselves before the soil-crusted feet of our new halfling overlords, and we will all be forced to call them hins. A final utterance before the soul collapses in on itself, and we all experience ego death.
Anyways, I like the point about just replacing speedies with wisps, but I offer a counter-argument that those goofy little halflings are basically the mascots of Arelith. If you get rid of them, you destroy years of tradition. Again, I'm not particularly attached to speedies, but I could see people protesting their removal because, "Arelith isn't the same," without them in some ethereal, vague, conveniently unexplainable way.