My limited understanding is that surge protection (AC suppression)is measured in Joules - the more the better. The best spike protection is auto shutdown - the faster the better. This is measured by suppression response time; e.g., < 1 nanosecond. EMI/RFI filtering effectiveness is measured in dB: 40dB being okay and 80dB being excellent.
On my 7.1 home theater system I have the incoming coax cable, the power chord for the cable box, 3 disc players and the LCD TV plugged into a Monster HTS 3600 surge/spike/line conditioner. The 130w x 7 receiver is plugged into a PSA Ultimate Outlet (line conditioner)which, in turn, is plugged into a Monster 6 outlet surge protector. The subwoofer is plugged into a Tripp Lite plug-in-wall surge/spike/conditioner.
On my PC 2.1 audio system I have the PC,the monitor, an external soundcard/DAC, pre-amp and amp plugged into a PSA Quintet surge/spike/conditioner. The subwoofer is plugged into another Tripp Lite.
I live in Tallahassee, FL, where in the Summer we have about 1 brownout a week. All of these units shut down eveything whenevr a resultant spike hits. We also have thunderstorms w/ lighening at least twice a week and I've had no dmagae done to my equipment.
The line conditioners have made no improvement to video, as far as I can see. However, the PSA products moderately improve the sound level and clarity on audio. The Monster 3600 does not.
Except for the Tripp Lites, these products are not inexpensive, but they are far from top of the line. If my budget were $200 I'd put it all into surge/protection. As far as line conditioning goes, I'd save my money for better speakers.