You've already mentioned Pocketbook - and I'd have to agree with you. It sounds as if you would get along well with a Pocketbook 302.
From what I've seen/heard about the device, it has the things you want, plus it's only $279.99 (comfort package).
I don't have a PB302, I have a Pocketbook 360. But, most of the software is the same (except, of course, you'd have it a bit different to run the WiFi and touchscreen on the PB302). And, it's very "hackable" software (Linux-based). Take a browse through the Pocketbook sub-forum and you'll see there's a whole bunch of stuff you can do with your Pocketbook, from adding different themes, dictionaries, fonts or even a highly modified FBreader program.
As mentioned, you won't be happy with PDF on a 6" screen - unless you re-flow it. But, you said you read mostly text - and I know FBreader, PDviewer and Adobe (all available on the Pocketbooks) reflow PDFs well enough. Not great - but I'm okay with my library books in PDF...
Give a read to this website (
http://www.pocketbookreader.com/PocketBook_302.html) and you'll see it supports a bunch of formats. Plus, it's just like having an extra hard drive - you can make many, many levels of folders - to your heart's content.
I've been very impressed with my Pocketbook. The software that these things run on is impressive. Can't recommend them enough.
Good luck with your search.
Marilyn