There are two issues here.
First, there's documentation of compliance with ESIGN's informed demonstrable consent rules. If you comply (and can prove it), then your e-documents become the legal equivalent of paper. ESIGN is no help. It doesn't require retention of anything. In the real world, however, we know that it didn't happen unless you can prove it happened. That means retention of some type of evidence of compliance with Section 7001(c) of ESIGN.
If your compliance with ESIGN is challenged in court, you will need to establish three things: the content of your pre-consent disclosures, affirmative consent by the consumer, and the nature and outcome of your "test drive." As you said, there's no need to retain copies of boilerplate notices. One sample of each version of things like the pre-consent disclosures should suffice--along with the begin/end dates of revisions. Affirmative consent is simply a matter of placing the right words in a document or message the consumer transmits to you. The "test drive" mechanism is best retained as a working demonstration that can be presented in court. Finally, you need some way to show that each consumer passed your test (the ESIGN "demonstration.")
After you have proven that you had the legal right to substitute electrons for trees, then you must turn to the second phase of your defense -- proving that you adhered to the timing and content requirements of the consumer regs (B, E, Z, DD, etc.)