Incidentally yesterday I created a simple exporter for (linux) coretemp, hddtemp and NUT's upsc: https://github.com/andmarios/sensor_exporter
Still slowly hacking on my homelab Prometheus bringup, but I've already got a start developing a battery level/power supply exporter. By far the most important Node information I want metrics and alarms on in my developer life! https://github.com/rektide/node_exporter/tree/export-battery
Almost went with a standalone Node exporter, but I decided I'd try some Go, and tour some of the Prometheus codebase. MustNewConstMetric is a very confusing thing to me, but hopefully I'm on the right track! Feeling double-inspired to get my homelab Prometheus up and going right now, between renewed excitement for these exporters and the 1.0! So close!
I started with the same path, using github.com/prometheus/client_golang/prometheus, but it exported too many application metrics (an order of magnitude more than the sensors I exported :p), so I went to a more custom approach.
It's a best practice to export all available metrics though, you'll likely run into situations where you'll need them. It's not that many time series exported by default which shouldn't cause any problems.