Premium Spectre Packs (PSPs) are good for getting your Rares maxed out faster. After that, I have found that regular Spectre Packs are best for gear/Ultra Rares. They also give you more and more useful consumables than PSPs. You can get up to four level 3 consumables in a SP and usually only two level 4 consumables from a PSP. Those level 4s might sound nice, but they're only ammo and a couple other things, so they'll basically never drop weapon amps or most of the armor upgrades.
Huh. That's not like my experiences at all. I get several amps and such from PSPs, but that may be because I've got full thermal clip packs.