In Amtrak's FY2013 budget (
http://www.amtrak.com/ccurl/345/484/AmtrakFY13-Budget-Comprehensive-Business-Plan-w-appx-052413.pdf), they used the services of a consulting firm with sophisticated models (read: monkey with a dart board) to break down the projected revenue increase in 2013 and identify which source is responsible for which portion of the increase. Their conclusion is that "Impact of eTicketing" adds $900,000 additional revenue during the 2013 fiscal year. That's less of an impact than "Improved Acela WiFI" (2.2 million), or "Impact of WiFi on short distance routes" (1.5 million), but still greater than $0.
Of course, the budget also says an additional $2.8 million is required in FY2013 to finish rolling out eTicketing to all ticketing and passenger scenarios. There's nothing that points to a reduction in operating expenses due to the impact of eTicketing. You would think there might be one, but might be currently offset by additional training costs or something. Even if there was a net reduction, I don't know if their consultant would know how to develop a formula to guess at that.