Especially in the beginning of the project it's not unlikely that the data structures getting pulled into the production templates will change from time to time, if only minorly. If that happens frequently, one might further augment efficiency by building a tool that parses the production templates and spits out debug templates with raw interpolation directives. (Possibly with HTML-escaped surrounding tags if they just provide the content for a tag's attribute, eg for things like the following.)
<img width="[% product.pic.x %]" height="[% product.pic.y %]" src="[% product.pic.url %]" alt="[% product.shortdesc %]">
____________Makeshifts last the longest.