Obfuscation of assemblies
Only if obfuscation does not decrease the quality and usefulness of (automatic) bug and crash reports.
Professional Security Certificate (Verisign/Thwate) - Authenticode signing assemblies
I don't think this is an important point for a BETA. If you can afford it, its a plus. However, it won't make your application more popular. Also, you won't loose potential users if you miss a certificate - whoever downloads and installs your application will not abort just because your stuff is not signed.
But there's another point missing: you need a fancy website. 'fancy' means: it must look professional, fit to your product and lead straight to a download link. The product needs to be easily installable - really easy. Small download size is also a plus in my opinion.
Writing blogs etc about the application features
Increases your google ranking, but needs to be used with care. If you fill hundreds of blogs, everybody will know it's YOU advertising your product. Nobody likes self-advertising. Let your users spread the word for your. A good application in a market niche won't need much advertising ...
Professional Icons/Splash and About screens
Is a good point to make the application look more polished, but the effect on potential users needn't be positive: nobody likes BETAs with awesome splashscreens and icons if they crash all the time.