I actually have Quiver and considered it but it doesn't seem to add images inline but I will have to mess with that some more.
Well, you can drag images into a Text cell. But, since the whole Quiver is based on cells, I think this qualifies as “inline” 
I have purchased DevonThink Pro and Papers but they were a bit more than what I needed in the end and just got in the way.
If you’re looking for something like DevonThink that does not get in the way have a look at EagleFiler. There exists an entire thread about the “DevonThink aggravation”, and I’ve posted a short summary of EagleFiler there.