My product desperately needs a bunch of usability enhancements but our sr. mgmt. only funds features that drive revenue. Any suggestions for paying down some of this technical debt?

Unless you’re losing customers or revenue because of those usability enhancements, they aren’t likely to get funded any time soon. The best way to get them into the product without adding cost or scope to each project is to give the laundry list to your engineers. Then, based on areas of your product that are under construction during any given project, let them determine which enhancements they can include without any additional cost or time to the project. Over time, you’ll whittle the list down and still keep it under the radar.