I am seeing the same things you are. Although I admit that I have gotten almost 4 decent years worth of service from my M70, I was hoping to coax a little more time from it. Bigger and better things lie ahead!
I don't know about that, but I was using v2007 as my main version only a year ago, and between v2007 and v2008 the resources required for the same assemblies really jumped up. Jumping from v2008 to v2009 didn't seem like quite as large a step. I'm not sure about v2010, since it won't run at anything beyond SP 0.0 on my machine (just upgraded from 32-bit XP to 64-bit Windows 7).
Unless you've got solid reason to upgrade, I'd recommend staying with what works.
I've seen (and worked with) some HP laptops that ran v2008 quite well with some very complex surface and solid geometry in 64-bit XP a year ago. Not sure the cost of those, but I wouldn't be surprised if they cost less than the Dell equivalent these days.