Hi snorkelfish,
You can see what is the changes in MP3, MP2, MP1 from this link.
http://download-llnw.oracle.com/docs/cd/E13218_01/wlp/docs92/relnotes/relnotes.htmlIn my opinion, if you application is running smooth on production, I think no need for upgrade.
Only in case that you face some problem in production and it can be solved by upgrade to MP3, you should do so.
Hope this help,
Sompol