I bought the Premium Gear (700 Steel) for the Berserker. I only got Gear with a Standard quality, but the info text says that there ist at least one "Gear of higher quality guaranteed". So that might be a bug. If it is so, I hope this information helps to fix it. =)
So, short answer is, it does grant higher quality gear (gear level), as you level up, but it's not till Rep 1 that it's even noticeable because until you hit Rep 1, you're getting 2s at best, which you get in normal packs just as frequently. That said, even higher rarity tier items (blue and purple that were shown on stream) are basically going to be locked till Rep 2 at the earliest by my math. At Rep 1 Level 8 Warden (character level 28 for those who aren't fully clear on Rep), I got a single grade 4 item from a premium pack and the other 4 were a mixed bag of 2s and 3s. Now for the good news, common rarity items max at 6, so you will see a new set of visuals by Rep 2 if my math is right (Each rep level is basically 3 levels of items from what I'm seeing) and Rep 4 respectively. Another bit of good news, Rep adds an item drop for each level up after rep 1, so even more stuff to break down or use for leveling gear!
Hope that helps clear that up a bit.
I found that it mattered what level my gear was. It seemed that when I had level 2 gear I would get some level 2 gear occasionally. I bought 3 of those gear packs and got 2 and 3rd level gear out of the last two. I was below level 21 when I did but I had upgraded all my gear to level 3 at that point with all the loot found. I seem to think it is based on gear rather than level but that is just my observation.