We do have good basic infrastructure, thanks. We use Puppet and have a decent deploy system that performs atomic deploys from Git.
We also do think in terms of services. But the exporter has to run somewhere. About half of our exporters are machine-specific (reads local stats from files or proc or whatever), about half run on the Prometheus node itself and talk to services like ElasticSearch or Postgres.
The problem is operational overhead of maintaining a dozen daemons per box, each with its own allocated port. It's not rocket science, just annoying. What could be a small script becomes something unnecessarily big. That's why we're sticking to "textfile" for now. When I have time, my plan is to write a small HTTP server that spawns plugin as subprocesses that emit their metrics via stdout, which seems like a much more reasonable, low-maintenance solution, and something node_exporter ought to support in the first place.