The types of applications I've created would never have survived without power users, so I do everything I can to keep them happy. If you're a developer, I recommend that you keep your power users happy, too.
Power users who love your software will talk about it in online forums, say complimentary things about it in their blogs and convince their coworkers to buy it. They'll make great feature requests, give detailed bug reports, help less experienced users get up to speed and provide an incredible amount of help during betas.
But there is a downside. You need power users, but power users can be the enemies of simplicity.
Power users will request features that nobody else wants, and they'll ask that existing features provide a ton of options that maybe 1% of customers care about. More than anything else, power users want to be in control of the software they use, so they'll choose something complicated over something simple if doing so leaves them in charge.
You might think you can ignore them and cater to mainstream users, but you risk having power users constantly deride your work if you create something they hate (Microsoft Frontpage comes to mind here).
So how do you keep them happy without scaring off new users?
It really boils down to doing what I recommended in part I of this series: figure out which features - and which options - you need to make obvious and which ones you need to hide. You can hide things that only power users want.
Most power users are the unofficial support technicians for their friends and family, so they understand your desire to keep things simple. Power users can accept that some features need to be buried beneath a menu or obscure setting, and they usually won't complain if they have to spend a minute or two customizing your software to get it to work the way they want.
By all means keep your power users happy, but make sure you don't increase your software's complexity in the process. Both sets of customers will be happier for it.