The SAM Ds also have a switch matrix feature which I thought was cool.
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There you go, I missed that (and I was actually looking for it.)
I'm actually a bit surprised at what Atmel are doing in their ARM line, and perhaps this prejudices me somewhat. To me, they seem to be a bit left-footed somehow in producing a line of chips which synergize well with their AVR line. For example, everyone seems to offer 5V tolerant IO pins on the ARM uCs-- except Atmel! That strikes me as downright odd.
It's been my feeling since the Due that the only reason to choose the ATmel ARM chips for the next generation Arduinos is because of the business relationship Arduino has with Atmel, rather than the technical merits of their ARM chips.I like AVR and I like ARM -- I'm just not been in love with Atmel ARM (so far, anyway.)
I think that's true across the industry for the ARM uCs, just amazing bang for buck, which is why I think they are becoming so dominant.
Yeah, I think ARM is ARM to a certain extent; you learn the architecture, not the manufacturer so much. I think what varies from manufacturer to manufacturer is the quality of the tools, though. Speaking of which, Atmel have recently released a new very affordable range of debuggers (the "-ICE" range) that cover both AVR and ARM targets. If I was going to get into Atmel ARM, I'd definitely spring for one.
Yup, which is why I suspect that the old 8-bitters will never die away completely. Sometimes that relative simplicity is a definite plus. Paradoxically though, they may get more and more expensive, relatively speaking!
I'm still at the beginner stage myself with the LPCs, but I've been quite pleased with what I've seen so far. My feeling is that everything has been made as simple as possible by NXP with the tools and online documentation they offer, and so it comes down to just putting the time in. Graynomad (Rob) has put much more time into the LPC stuff I think, and he seems to making good progress with it.
I think you are right that LPCOpen is roughly equivalent to ASF, but I haven't really got into that as yet. I should really decide to do a proper project with one of these things. Learning seems to accelerate quickly when things start to get "real". 
Definitely check out those new -ICE debuggers if you haven't already. The only thing I prefer about my AVR Dragon is that it can also do HVP, which the new debuggers can't (they can only do serial and JTAG programming, I think.)