"it's now feasible to create all kinds of experiments, test fixtures, visualizers, analyzers, and support software you never would have had time for before, which you can use to improve your process and create a better product."

Yes, yes, yes, so much yes. Log analyzers, consistency checkers, performance evaluators, all sorts of hooks and helpers, precisely of the "single-use application for a single user - what a luxury!" sort, which made the entire development process so much more secure and comfortable. Most of the tedious moments (looking for a single bad value in a heap of logs etc.) went away.

The scaffolding I have now is a castle. The scaffolding I had a year ago was a log cabin. Nothing against log cabins in general, but castles are a lot harder to break into and have fewer holes for problems to sneak in.