Have you considered the other way round? You could just have a laptop and use a docking station at home. Then you only have to keep one PC up to date. And laptops are so much cheaper than they used to be.

Just a different perspective...

Or get a small, portable, all-in-1 desktop. If you're mechanically inclined, you could do a really cool project. Use a small AM2 motherboard like this and take apart and integrate a keyboard and LCD monitor into a custom-built case, and you have an amazing, cool, all-in-1 portable computer.

Of course, that's a huge project, and you probably don't have the time, experience, and money for something like that.

Do you really need to stay on top of hardware? Just get something mid-range to high end and use that for a few years; by then there'll be a new RAM standard and CPU socket, so you have to get all new components anyways.