This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
It really depends on the application. If you convert the result sets to objects, and find that you need to keep maintaining your JDBC layer and that it is growing in size and complexity, it is probably a good candidate for being migrated to JPA. On the other hand, if it is pretty much doing what you need it to do and you are happy with it in terms of its performance and maintainability then don't change what isn't broken. JPA becomes advantageous for applications that have data that maps to object graphs (with relationships), that execute multiple kinds of queries over the objects, and that regularly navigate the object model. Because JPA providers do a lot of caching in memory, JPA tends to perform better than JDBC when there is more object reuse.