If LL wants to improve new customer retention then they have a choice. Either police the welcome areas or delete them all and dump new customers into estates with staff on hand that keeps the antisocial people out.
Period.
The rest of this discussion is not going to help since it is impossible to preinstall the entirety of a massive dynamic virtual world on a computer. Just putting part leads to disappointment as soon as new customer try to escape the new customer areas.
Get rid of the griefers in the welcome areas. File criminal charges if they return. Otherwise accept that the griefers decide LL's fate and go on about your business. If LL doesn't want a couple hundred 4chan/SA goons deciding their financial fate then LL can grow/harden up and deal with it. LL has managed to dispose of a group of them that were trying to destroy the forums so LL can man up and get rid of them in world too. Even if they are friends/relatives of Lindens.