When to split?
I'm at bar18 of 30. What are the factors pro/Con splitting? I don't really care to have a second hive.
Re: When to split?
Gives you a second hive. This is something I highly recommend to just about everyone, as having a second hive gives you resources to steal so you can "help out" your first hive, whenever there's an issue. Also, gives you 2x the bees, to produce 2x the honey next year, and is often used to prevent swarming (although I personally think that's going about things the wrong direction).
You need to have equipment for the second hive. Other than that, with 18 bars built-out, there aren't many other real cons. You're not all that likely to get a honey crop this year either way, and 9 bars should be quite sufficient for over-wintering over there IMHO.
End Result (IMHO):
If you want a second hive, now's a great time to get it going. Otherwise, if you're sure you do NOT want a second hive, your bees should be fine "as they are."