Speed messengers shouldn't be able to just find people. I get they're part a "organizational tool" but they also make the world too small and it feels like they ignore a bit of the limits of the world.
So have these guilds services blocked by common anti-scrying methods because how else are they finding you by name?
Further it makes people who livelord in their anti-scry bunkers unable to freely receive information and so have a reason to either involve more people (messengers, people who receive messages for them), but increases the chances you can find them.
"The Wisp messengers" could be turned into a premium service that operate similar to player wisps.
I also get that you can "pay" but the time limit is a bit silly and this would put more control into player's hands and make rping with humans a bit more meaningful.