How to chase fewer signatures in tax season

Short answer: one spot at a time, a quick check before sending, and fix only what's wrong.

Get engagement letters and 7216 consents signed before the season, not with the return.
Send the 8879 with the return and ask clients to review first.
Send spouses separate links.
Before sending, check that fields aren't swapped, every signature has a date, and nothing is on the preparer's lines.
Remind after three days.
If something's wrong, send back just that spot.