* The actual MAS store app itself is a horrible piece of garbage wrapping a bunch of web views. Just make it a real native app and rewrite it.
* Sandboxing is great, but there will always be things that fall outside the sandbox. Have a "Power User / Developer Tools" category and associated checkbox in iTC that says "My app needs to opt-out of these parts of sandboxing". Put those apps through a much more strenuous review process.
* Relatedly, add more entitlements to the Sandbox, even if they also trigger a more in-depth review.
* Both iOS and the Mac app stores desperately need feedback mechanisms and some basic customer support tools. This has been obvious since at least iOS v4. I can only imagine this is due to Apple's inability to do good server-side software (and the organization doesn't value it like they value client software). This should automatically give you at least a private way to send a message to users leaving a bad review, then prompt the user to update their review if the response helped them. Asking users to review is hard enough... getting them to update a 1-star review is nearly impossible.
* Hire more reviewers. There is no excuse for reviews taking so damn long.