I'd recommend it yes. Kohana is a bit of a hackers framework - you do need to dig inside it sometimes (I consider that a good thing). It also has a pretty nice ORM based / Role based auth module included which you can extend fairly easily.

In terms of LTS: V2 is pretty frozen at 2.4 right now (i.e. no API changes) though the documentation still reflects V2.3. There should only be bug fixes on the 2.x branch. 3.x is in active development (and worth looking at) and should be there for the long haul.

I personally use 2.x because that is what I started with and I haven't had chance to make the switch to 3.x (it's pretty much the same except there are changes to some naming conventions and file paths) mostly due to having to support 2.x based sites still :)

EDIT: It's a bit old (and I apologise for the abysmal writing!) but this is a comparison I wrote when I first made the switch: http://www.errant.me.uk/blog/2008/06/framework-comparision-c... might be useful.