I agree, in normal operation with lightweight apps, the RAM isn't much of a problem – but don't try to, for example, use the amazon kindle app for android. Apart from having horrible animations, while it sometimes works, other times it just crashes. Normal browsers I tried (chromium, firefox) wouldn't work at all. (I have a different launcher + a floating menu button thingy for 'advanced' usage running, as well, though.) And also the thing with selecting dozens of pages of text in FBReader by accident I described above.

Different resolutions really are a matter of taste, of course: For me personally, a higher resolution really makes a difference. But then again, I'm the type of guy who already flinches when he sees printed things with visible pixels (like cheap ads in the bus or menus in a snack bar, you know the type) – when reading, it's really a bit distracting for me. With 303 dpi (and the right fonts installed) on the other hand, I find myself mostly only missing the smell of real books, otherwise it's absolutely fine. It even feels to me to be less straining for the eyes, but that could be something like a placebo effect. Also, my parents both have low-res Kindles and don't see any difference, so this is obviously not a problem for all people, it's just one that's very important for my own experience.

For energy consumption I'd imagine the "missing" backlight to be more relevant than fewer pixels, but even with it (I'm only using it only on low brightness and when it's dark), the battery lasts for weeks with moderate to heavy usage. I'd expect the same from all current e-readers, to be honest. That's not to say it's not true that fewer switched pixels can use less energy, but especially with most animations disabled, I can't imagine it to be a really big deal for reading.
A low resolution might put a bit less stress on the slow CPU for rendering stuff (and considerably so on memory when dealing with big images), though.