A new computer might become a downgrade
Earlier today, while reading a piece by Tim Bray, he considers giving a try on a Chromebook sometime.
Sometimes, going minimalist is good, reduces the hassle and lets you focus on getting the job done but this is good if the tools don't get in your way.
Replacing a good computer, even one that is a little old, like the one Tim pointed out that is "getting out of gas" with a brand new and crippled computer with slow CPUs, low memory, limited or not existent applications and depending on network connection is not a step up, it's a step down.
Think about it the next time you consider a Netbook, a Tablet or a cheap computer. Think about your needs more than the form-factor or the market trends.
Buy a machine that "gets your job done" with minimum hassle.