So this idea is pretty much set in stone. Exos will have 3 phases.
EXO SPAWNS. The spawn system will have colors preset that it will choose from then a handful of rare colors to choose from each time. No color will be used than 2 times in a row on any element.
While an Exo is active all the planets around or in a specific distance has increased meteorite spawns.
When the Exo dies ALL resources are generated into a meteorite that you can actually portal too. This will be composed of a hodgepodge of some normal blocks and the gems, ores, Lucent and other ingredients and will last until either mined to the core or the time runs out.
If any gems, ore, Lucent and other rare resources on the exo will fall in meteorites on the planets that where closest to the Exo and the rare resources will be in the meteorites that fall until they are collected or the time runs out.
This allows for more of the rare stuff to be collected before disappearing!