I feel like this could be a good pain point to market to people. Typos happen to everyone, and I don't remember any other ESPs advertising a feature like this.
Would it be possible to have some kind of validator to cross reference the dynamic content tags in your campaigns with the existing (default & custom) fields in your account? For example, if you need %%First Name%% and your campaign somehow ends up with %%FirstN ame%% or some other kind of typo, there would be a popup saying:
"Warning, this campaign contains the following invalid dynamic field(s): %%FirstN ame%%. Are you sure you want to proceed?"
and the options are:
"Yes, ignore this warning and proceed." "No, take me to the editor."
If you could find a way to have it catch a space between them (% %First Name%%) or even a missing % that would be a great bonus, but from a coding standpoint I can understand if it's just limited to an exact match of the characters between the pair of %% tags.
Great Idea, however, we always always recommend first sending a test email to yourself to double check your email, including proper Custom Field values.