If deleting Snapshot 1 of EBS still allows you to restore Snapshot 2 and only the data delta is saved in 2, is it a cost save to always delete Snapshot 1?
Snapshots can be seen as a collection of pointers to the actual data. The moment you delete Snapshot 1, its underlying data is preserved and "incorporated" into the next most recent snapshot (Snapshot 2). So to answer your question, here is a snippet from the documentation:
"Deleting a snapshot might not reduce your organization’s data storage costs. Other snapshots might reference that snapshot’s data, and referenced data is always preserved. If you delete a snapshot containing data being used by a later snapshot, costs associated with the referenced data are allocated to the later snapshot."