Advancing through tiers doesn't seem to be rewarding at all, and after awhile it gets really repetitive. The only two really other things to do is building and exploring, but you have to grind a lot to make something look good, and exploring doesn't really get you good loot.
After getting to tier 10 planets, the chests I found were incredibly stuffty. Hard-to-get chests contained weapons three tiers under, low leveled ore like iron or small amounts of pixels.
The only real good loot at higher levels is tech :v