I level the LIs, if a slot is free, to lvl 60 and deconstruct them. You can store the atributes, but consider, as above mentioned, they are just usabla for a max LI level, depending on the LI they are taken from.
If you destroy a lvl 85 3rd age LI with max level you can get xp runes between 300-900k and some tier 7 relics. I keep the 800 and 900k ones in storage and use the smaller ones for the next LI. This way you can max your 2nd/ 1st age LIs with one xp rune to lvl 30+, change the attributes to the ones you desire and keep leveling the LI to max.
The benefit from changing the attributes after reaching lvl 30 is, that you can raise the desired attributes while leveling your LI, not the random and maybe undesired ones.
Furthermore you will have the needed relics for your LI.
lvl 85 lm (main), lvl 85 champ, lvl 85 rk, lvl 85 hunter, lvl 85 minni