I too have been baffled by the lack of popularity of these devices. Most people have never heard of them, so there is a problem in the marketing. When I bought mine many years ago at BestBuy, the sales person really didn't know what the heck it was. (I had read about it on the net.) Yet I have introduced the Roku to many of my friends and they all have come to treasure them.
I often peruse Craigslist and Kijiji for Soundbridges, and I now have a couple in reserve in case mine dies on me. They go for around $50 to $75 where I live. But the Soundbridge is pretty solid (with the exception of the power adapter) and mine just keeps on going.
My biggest fear is that the radio database will be shut down. This will effectively destroy half of the Soundbridge's usefulness. My hope is that the success the company is having with video streaming devices will keep the company alive for a long time.
I had thought about the Squeezebox as an alternative. But it to relies on a company-run database too.
I have tested a solution that works well in case we are all stranded. I have a cheap $100 Chinese noname android tablet, and using an app called Tunein Radio, you have an up to date internet radio solution. I just plug a cord from the headphone jack into my stereo system, and voilà! Any tablet, android or Apple, will work. There are also apps for streaming content from your computer.