Based on discussion with some of the woodworkers on /r/woodworking, I opted to forego the pre-stain conditioner.
I went again and stained the entire back rest with the dark walnut gel stain.
Doesn’t look like Dark Walnut on most of the pieces though, eh? This is because, as I mentioned before, all the wood was second-hard from a friend of a friend’s bookshelf. I’m not sure if he had stained it previously or it was just the natural aging of the wood, but the color of most of it wood was significantly darker and had a bit of an orange hue versus fresh pine. I do like the way the dowels absorbed more stain and are contrasting nicely.
Even after liberal (and I mean liberal, most of this project has been spent sanding) with 80 grit, I was unable to completely get rid of all traces of whatever was applying that orangey hue. This is where a thickness planer would have come in handy!
Oh well. I think it looks alright so far. Next step, stain the seat. Then 4-5 coats of poly, sanding with 400 grit in between coats.
-- Tim Bridge, Northern NJ,"Education is when you read the fine print; experience is what you get when you don't." Pete Seeger