The judge of value comes with increased quantity of joules of energy it can absorb and the speed with which it can react to the noise/surge spikes. I tend to use stand-alone boxes rather than an in-wall receptacle since you tend to need multiple things plugged in anyway and would need a power strip. There are some quite good units out there, and some look like a component rather than just a big power strip. I've also got one wired in at my power panel that helps with the more mundane things in the house. Keep in mind that more and more things have SS devices in them from p/s to other electronics, including your stove, frig, microwave, etc. It helps to protect them as well at th epower panel. If you want to go even better, you get a sine-wave UPS, and connect everything to them. These only use the line voltage to keep the battery(s) charged - all of the power is generated in the box for the load. This is probably the most expensive option, though.
I like the flexibility of a plug-in device, it's easier to change or upgrade should it need it down the road. The wired stuff rarely goes on sale, but the plug-in stuff often does.