I had a Powerseller status for about 4 years. As I look back, I'd say it was a total waste of time. It's just another "eBay Cheerleader" device to make you become more of an eBay slave. Gotta keep working hard or you'll loose your status. sell sell sell.
Back when I had it, they didn't have the computer watching you. You didn't get threatening emails that yours sales were down and "unless" you get them back up again you'll loose your Powerseller status. Those email started at the time they took it away, but prior to that you could ride through long slumps and still have it.
I'm glad they finally took it away. One less thing to worry about. Now I just sell at whatever capacity I can and don't worry about whether eBay is watching my sales volume or not. All it ever did was give me a quick response to email queries, and we ALL know how useless email replies from eBay are. If I was ever invited in again, I'd decline.
I used to display the logo. I can't say if it ever increased sales or not. Take it as a personal accomplishment that you're doing good, but don't fall into the "eBay Slave" trap.