I'm running Gentoo with the default SysV-style OpenRC init system. The boot time is short enough to not bother me. Is there any reason to try systemd?
Systemd is pretty cool. I think a lot of users resent it just because it isn't SysV init -- I certainly did for a while when fedora first adopted it (I could care less about faster boot times too). Unfortunately, my resentment was so deep that I did not bothering to learn about it, which made the issue worse.
It probably is something someone should write a nice, friendly tutorial or guide aimed at the (non programmer, non sys admin) general user. I think there's a bit of an unacknowledged elitism in the linux world that way -- although to be fair, this is a maybe a consequence of scarce resources.
I haven't used gentoo in a while and I don't know the status of systemd there. If it doesn't matter to you for now and you have better things to do beyond pouring over the docs, then don't worry.
Ther are multiple advantages of running systemd even after booting is done, some might interest you, some might not, a quick summary:
for more information i redirect you to the systemd homepage