I don't believe there to be any performance of maintenance banefit from separating indexes and tables into different tablespaces -- look at asktom.oracle.com or the google forums for many discussions on this.

I've been following advice and putting objects in tablespaces based purely on their size for quite a while now, and it works great. Maybe a dedicated TS for a particular table, of for different partitions of a hash-partitioned table, but other than that make it simple for yourself.