When the primary election for a party's nominee ends in a toss-up or close contest, wouldn't it be smarter for a party to nominate the candidate that is more effective in general election swing states? And is there any precedent for parties doing this? Or is success in primaries not indicative of general election success?
Generally, the major parties tend to weight states they do better in higher. After all, the Republican nominee must firstly appeal to most Republicans, and visa versa. Also, primary voters aren't necessarily representative of general election voters. For example, Independents who vote in Democratic primaries aren't (for the most part) swing voters, instead, they consider themselves more liberal than the Democrats.
So, to answer your question, purple states are not given outsized importance during a nominating convention, nor would it necessarily be helpful to a party to do so.