Unstable cores are an issue the higher you get. Especially if you spent time farming the loot cave for Aion Adapter armor, which ONLY drops at 200. Sure, I can do Sieve and get it up to 300 (because Kepler does NOT drop beyond 300), but then it costs 10k if I want to infuse that up to 450. It ends up being cost prohibitive to level up a few builds to have ready for master raids, dungeons, or the unexpected to improvise on the go. Especially when power level matters and you don't get brought up by others. Or worse, you're the one people are relying on to bring up their level. Like when I'm helping other clan mates and friends through higher content. I consistently try to keep 60k cores on hand at least, but upgrading my titan for the epic raid gutted my cores. I went from 120k down to 20k just to have 2 titan builds and a warlock build ready to go.