Vrana will likely immediately get an opportunity to contribute in the top-six of the Blues, and can hopefully regain his form there. Vrana's only played 5 games this season, but in 26 games last season, he scored 13 goals and 19 assists. Vrana's an elite goal scoring threat, and if he can consistently stay healthy and active, this deal could be a massive success for the Blues.
However, there's a reason the price was so low for Vrana. For a cap-strapped Detroit team, his $5.25M annual value for this year and next was too rich. Sending him to the Blues, the Red Wings will also be retaining 50% of Vrana's contract.
The Blues acquire a young forward with elite goal scoring potential as part of their re-tooling year, and the Wings give up on a young player for salary reasons. This trade is a clear win for the Blues.