[Spiffy]

None of the above.

Missing from that list is improved firmware, featuring more solid and logical on-device management of ebook files.

That could be called expensive in terms of development resources, but its cheap in terms of actual effect on the hardware. Keep the hardware cheap, without unnecessary feature clutter. But file maintenance is less of a feature and more of a necessity. It's not like Wifi or 3G, which are total gravy which other companies are trying to persuade consumers are absolutely necessary. They aren't.

Although Wifi may not actually be that expensive to add, come to think of it. The chipset isn't very expensive and there are no ancillary costs like with 3G. The problem is that I bet Wifi would affect battery life... so why bother? If its added make sure its not an "always on" kind of situation and has to be manually turned on.

Larger screen? Great. But maintain the smaller cheaper ones as well on at least one model. Anything over 6 inches isn't NECESSARY, its a luxury, but its certainly more worthwhile than most "features".

Keyboards? Hell no. Why? Just why?

Keep the SD slot. I don't care if the unit could be $10 cheaper without it--you need it.

Sealed in batteries are stupid. I'm not sure how that's a cost issue though. Are sealed in batteries CHEAPER to produce?

Backlighting is an interesting question. I honestly don't know. Don't need one with the current model, but I can conceive of designs where it might be a good thing. Just don't go adding a touch screen, okay? Too little bang for the buck. Ditto for color screens.

A reliable clock would be nice, and I don't think it has to cost much. Don't have it drain the main battery. Have the clock run off its OWN standard watch battery (make it an easily available affordable type, coin sized or smaller), and have THAT battery accessible via an externally accessible panel which you don't need a screwdriver for. If it added more than $5 to the cost of the unit in total I'd be shocked.

So here's what's important:

Absolutely essential:
1.) Reading your books
[fairly large gap]
Fairly essential:
2.) MANAGING your books
[gigantic gap]
Somewhat essential:
3.) wide format support, accessible battery, SD slot
Nice to have, if it doesn't increase cost:
4.) having a working clock, case colors (as opposed to a color screen)
Reasonable luxuries, if increased cost is not huge:
5.) Wifi (but just for file transfer, not for web browsing or any other crap like that), screen bigger than 6"
Unnecessary or maybe even detrimental "features":
6.) 3G, Touch screen, Color screen, Keyboard

Another thing besides file management not on the poll is a feature similar to the Pocketbook 360's accelerometer page turning feature. It actually sounds more useful (and cheaper to produce) than a touch screen. It's probably not an expensive device if they can add it to cheap video game controllers. I'd rate it like "Wifi"--potentially useful, but only if its implemented correctly and doesn't add much cost.