I think the issue here is first to define "big". What does that mean to you, size of an OS kernel (2million lines) , size of a big application (500,000 lines) etc. That gives you an idea of how much time a rewrite will take.
Next define the problem, why do you care how it is written: is it because you are not confident in the results or it crashes often etc., are you extending it to something else or adding functionality, or maybe you need to maintain it in its current state and just fix use bugs, or do you need your users to understand the code. [The latter is encountered say in scientific software, when you may need the users to see that the code implements the algorithms correctly]
The you want to define how complex the field of the program is, is it highly mathematical were algorithmic errors are likely, or maybe numerical rounding errors etc, or is it simpler [in algorithmic complexity] e.g. a GUI.
Once you and we have some of those answers this discussion can go forward. I seem to think that you don't need a c++ standard but more likely to want a static analysis, e.g. like the converity systems [note: useful but very very expensive]
Beyond that, I agree with the posts above, there is no such thing as "the standard", but a lot of things in a code that make me worry and the first one is lack of consistency. After that, poor use of const, lack of references, poor variable/method/class names, lack of comments [particularly around algorithms], overly larger dependence trees etc.
Layout etc, is nearly irrelevant, because I just pass it via a layout manager and it formats the code the way I like it. (e.g. opening/closing braces lined up etc), whilst other developers lay the code out differently, that way the team all work on code in a format they individually prefer.