Snapchat is oriented towards creation. When you open it, it starts on the camera.
Instagram is so much more self-regulated and bound in crafting identity. You're right in that it's much more focused on consuming since the barrier to posting is much higher than snapping.
The only few times I used Facebook's "My day", I just posted my saved snaps. (and I only did it to see who'd open!)
I don't even use the regular camera app. It's always Snapchat. It's the best casual camera app out there.
Not sure I would call it creation when going through 10 minutes of Stories from friends @ Snapchat...
There are a few issues though I have noticed:
* Cards can sometimes glitch out. I've had overlapping cards get stuck and had to restart the app a few times.
* Bios take a long to load compared to photos etc. for some reason.
This is the key thing. While I don't use any of their Snapchat cloned features, I do think their photo product is very good. So you can see what they are doing to users like me. I'm now more likely to use their stories because I already like the core product. Also, celebrities have a higher reach on Instagram than on Snapchat, so the transition for them is seamless while also maintaining (and increasing) their existing follower base.