A cold one which is growing (with scheduled batch ops) but indexed and UPDINDEX=true (for rare update operations that still might occur) and a hot one for realtime data which has no index but whose size will be reduced and kept constant.
This makes perfect sense. You could also think about keeping your large database(s) completely static. The UPDINDEX option will keep your index structures updated, but it doesn't update all database statistics, which can also speed up your queries. But you can simply run some of your queries, or compare the query plans, in order to find out if queries are evaluated slower after an update.