I disagree. First, 8GB for $50? You don't consider that cheap???
Not all that long ago, it was $125 per GB! RAM prices have been in virtual free-fall for years now, and the quality of the product and its speed have been constantly improving.
And, yes, you can buffer for future tech improvements. My PC was built over a year ago and is still ahead of the curve. I built it myself so I could pick and choose which components went into it while keeping price down. RAM is one area that will help. For example as OSs and programs gain more and more code bloat they will require more RAM over time. By having RAM now, I don't need to get more later. Also, with x64 architecture, you get much more RAM addressing, but because of this every program you run requires more ram to run by default. Think of it as the allocatable blocks are larger, so even if a program uses a minimum of RAM, it still reqires X amount. That amount has increased as compared to the x32 architecture. Overall this is worth it, but it is something to keep in mind.