I don't see any point in maxing out your storage if you have enough space already. Just go for your Nanaly summons but don't expect anything because the increased chance only means you have a higher chance to get Nanaly IF you actually get a black unit, which is still around 3% :P

Anyhow, it depends on your storage, but as i said, i do not see any point in maxing out storage if you have a decent storage amount already.