In my last job, we did both and used the latter as part of our pitch to migrate customers to newer architecture. In order to justify the R&D, you have to show a benefit to your margins or the time spent has less value. Not everyone will share the savings with their customers, which is why doing it is good for sales. Show the customer you care about their spend and not just your own.
As always, "it depends." But for those that are dubious: VCs generally dont like companies that have super high gross margins, because it signals you might have left growth on the table.
In general, if you set your original pricing to yield an acceptable gross margins % and you cut your costs by 10x, you pass roughly that on to your customers if you're being smart