undo tuning in a multi-purpose database

 I have inherited the administration of a 10.2.0.4 database that has 2 different purposes.  One set of applications/tables run about 90,000 small transactions per hour into the database, which are then purged back out on a 3 hour rolling window.  The other set of applications/tables operate as a data warehouse, where large files are loaded in via batch processing, and reports/data analysis are run on daily/weekly/monthly/yearly periodic basis.

I think one of our main tuning issues is that undo wants to tune a large space because of the many small transactions that occur while the larger reports/queries are run.  My question is - are there reasonable things to do with tuning to get these 2 applications to live together?  Or should i just spin the small transaction based application into it's own instance, and then tune each instance separately to optimize based on its activity?