Finish building models or buy new battletomes/codices? How often do new editions come out?

I’ve been in the hobby for a few years but haven’t gotten a chance to play the tabletop yet. I collect an army for AoS and for 40K, but I still don’t have enough for a 1k point game in either.

I thought my battle tome for AoS in like the beginning of 3rd edition, and just never got around to completely my army due to time and money.

I’m finally working on my pile of shame, and I’m thinking of getting the battle tome and codex of my army in each game, but I’m not sure if I should. I already have one battle tome I never got to use.

Plus my AoS army lost its start collecting box, and it was really good. I would have bought a second one if I finished my first one in time.

My armies are Ironjawz and Chaos Space Marines, if it matters.