At the risk of echoing some of the earlier comments
I have had my vanilla PB 360 for just over two years. It cost about 100 GBP back then, and the price has been pretty stable since then (even with newer models). This is vaguely reassuring. Rarely see them come up on ebay second hand, too. Size is perfect, of course, but I'm assuming that's why you're looking at this range. A friend had the similar-sized bookeen, and liked it, but I didn't get to play with it much. It *felt* a smidge longer, but that may just me being sizeist. The size of the PB360(+) manages to fit every pocket (jacket, jeans/back) that I need.
I bought a 360+ six months ago for my other half - she loves it.
I can say that I think the matte colour (blue) of the 360+ is a bit nicer than the patterned black 360 - but it's not something that would sway my decision. What *would* is the fact the 360+ is significantly more responsive when moving around menus. Page turns are slightly faster, though I'm so used to scanning ahead the last few words on a page, and am used to the speed turn of the vanilla 360. It's faster than a paper book
No idea on the 360+ NEW .. I *think* a friend got one, but we had trouble working it out from the About/System information.
Button clicks on the 360+ didn't seem measurably quieter than the PB360 original. I tend to use the 4-way rocker navigation for moving between pages anyway, especially if I'm reading in bed. There's the accelerometer plugin that lets you move forward by flicking your wrist too if noise is a big concern. I found the noise of me swearing every time I scratched my nose and jumped forward a chapter out-weighed the noise of the buttons.
For vendors - check greenreader.co.uk (they're based in Ukraine I believe). They're very helpful and would be able to tell you when they can get them in if they don't have them on stock.
I've also bought gear from ereader-store.de - they have good prices (though they did mislead me about what they actually had in stock at the time I bought something from them).