So, what's my reasoning on upgrading and purchasing computers and parts?
Back in 2009 I bought my current computer, which is quite a while ago if you consider the fact that I'm a computer enthusiast and a gamer. At the time, I bought the cheapest quad-core money I could get together with 4Gb of DDR3 memory. It was a very cheap, yet powerful, setup. One and a half year later, the on-board audio controller on my motherboard broke down, and I felt the need for more capacity, so I purchased an USB audio card, additional 4Gb of RAM and 2TB worth of hard drive.
I upgrade in two scenarios; either something breaks down and I replace it with the most cost efficient alternative, or what I have doesn't work for me anymore and I have to get something better. In my opinion, it's not worth chasing 5-10% upgrades, or to get top-notch equipment. Spending half the money on 20% less performance is wise. When upgrading, you want at least 30-40% increase in performance.
When I upgraded my computer the last time, it was because I needed an audio card (obviously...) and because my 4Gb of RAM wasn't enough. I got an USB audio card because it's both portable (can be used in other setups later on) and because it was the cheapest solution. An internal audio card would have been more expensive, and I wouldn't be able to use it on laptops or such, meaning I might need to purchase one anyway later on. As for the RAM, it was a cheap solution to get rid of the SWAP file, reducing disk load times and clutter. Nowadays I mostly use around 6Gb of RAM when working.
I also bought two Samsung Spinpoint disks, each at 1Tb size. This was a bad purchase, mainly because the bad quality. One of the disks, the one with the OS on it, is making giving me the red warning light. Earlier I've had CRC (checksum) errors. Sometimes data can't be read properly, sometimes I can't write it properly. For now, my system works, but it's never fun to see software and games break. I've manage to salvage most of my working data, though.
I looked at SSD disks before, but I couldn't justify the price vs size. I've seen huge improvements in both speed and stability since then, and seeing how the disk is my bottle neck right now, it seems a logical choice to get a SSD. With a faster system boot and application start, my new bottle neck would become the processor, which has at least a year left. Then, in a year, I could get a new platform, migrate my gear, and use this setup as a server. This is how you save big money.
You should always get at least a three year warranty on your components or computers. Some parts won't stop working after a while (like a bad HDD).