Agreed. It is useful to pass things that a legislature may never pass, like term-limits for legislators.

In Washington State, the initiatives frequently yield legislation that has conflicts/dependency problems with the existing law, something that happens far less-often with bills from within the legislature.

Also agreed that a high signature-number bar is one of the simplest/expedient ways to limit ballot-initiative spam. We have a person who has successfully made it their personal mission/job/source-of-notoriety to place some sort of small-government initiative on the ballot every year.