While I can't say I entirely agree with Renan's interpretation of new users who experience the negative impact of a poorly formed question, I do agree with him entirely on the fact that the sandbox should be more readily discoverable and I would support any attempts to do so.
I'd actually take it a step further and say that it should be an intrinsic part of the site.
New contributors should all have the Ask Question button pointed to the sandbox by default, where they can get the help they need and then there should be an option based on either a voting system or a single user with sufficient rep to graduate the question to 'Prod', so to speak. In other words, new contributors shouldn't (in my opinion) be able to get to the main site and the negative commentary in prime; they should be routed through the sandbox in the first instance.
I'm not currently sure how long the 'new contributor' flag stays on a new user, or whether or not we should be able to flag someone based on questions only (not rep or answers, or votes, etc.) as being routed to the sandbox, but it is my view that it should be an intrinsic part of the site that new users experience prior to their questions being released. This could be managed through the conventional queues that we all get as it is and users of sufficient rep should have the 'sandbox' queue come up so we can work on what goes in there regarding new content in a supportive way.
Will that discourage some users because they don't get their post on the site in real time? Perhaps. But I'd argue that getting your content up in real time and getting it criticised is even more discouraging, and SE can take some getting used to as a community whether we remember that or not.
So; my proposal to SE would be that the sandbox become a queue that can be enabled on a site by site basis by those responsible for it; if enabled, the question is written up and is basically suspended (made invisible to the main site but put up on a queue) for review. Once people on the site are happy with the framing and layout of the question, it is released, making it visible on the site (preferably with a 'cleared' message naming users, much like the one we have for On-Hold right now).
This would mean that it doesn't rely on threads in Meta, or any other content driven medium for delivery but would be built into the behaviour of the site directly. That would put a greater burden on our senior members and Mods, but it would have the following benefits;
1) Less poor quality questions on the front page distracting browsers from the quality content
2) No longer would we have a sea of On-Hold questions through the site, making us look unwelcoming
3) Prior engagement between new users and senior members of the site in a supportive framework before a question goes live; they get to know us a little before we pull their question apart in front of their eyes.
Whether or not this can be done easily is (to me at least) the real issue. I think it is at least worth the ask given the value that could come of it in terms of image let alone better quality questions.