Actually I built these machines with parts I had lying around. As I only had 1 GB RAM sticks (and 2 RAM slots), well 2 GB I have. But as I said, I have quite fat systems and for what I need (text editor, xterms, firefox, a little LibreOffice and GIMP from time to time) it doesn't make any meaningful difference.

A few months back I had a 2004 vintage machine with 1GB of RAM and the main annoyance was that firefox was quite long to start up in the morning, and that's about it. Ah, and spamassassin was a tad slow, too, meaning that my emails needed a few minutes more to fetch in the background, no big deal. I switched because the graphic card failed and I hadn't any AGP card anymore :)

To be fair, on modern systems, memory doesn't just "sit there being unused", especially if you keep the system running for a while. Memory not used by running processes will be filled with cached files from disk. Adding additional memory can result in significant improvements, depending on your workload and other hardware.

Whether it's worth the money is a personal decision, of course. It sounds like the GP doesn't use an IDE for development; I've routinely filled up 2GB even on relatively small projects just with Eclipse.