Thank you for your insightful response. Our backup needs are far more modest than what you deal with at a university. We have only a few gigs to backup and a limited budget for tapes.
If I understand your definitions: Latency should be within 24 hours. TTL, a week.
My primary concern in using an incremental strategy is having to step through multiple tapes should a full restore be needed. Had a bad experience once on a Unix box when we encountered media errors on an incremental archive while restoring after a major upgrade. Wasn’t using Retrospect at that time…