Obviously keeping several different indices has a negative impact on insert and delete performance. How about query performance: Does it make sense at all keeping too many indices on a table? Will the query performance improve in any case with an index added (of course for queries using the index at all) or is it even possible that the query performance will degrade with too many indices because it becomes necessary to consult all the indices to get the result?
In case there are different indices on a table: will they all be considered, or only the best from the optimizer point of view? Does Oracle implement multi-dimensional indices?