AirPort Express no power-on - can it be repaired or replaced?
I don't believe that the Airport Express is considered a serviceable product. As you have seen from the repair sites it isn't easily opened. A repair from Apple isn't likely to be available or cost effective. It never hurts to ask though -- especially at the Genius Bar where they have some discretion depending on your situation.

Without destroying the exterior, you are likely faced with getting a replacement. You could save some money by buying a refurbished Airport Express from Apple. And perhaps even sell your old one for parts on eBay in case someone else wants to split it open.