Themes

It's the cache rebuild that takes the time (Or at least the re-rendering without an existing cache), so using cron to clear the cache every minute is probably not a good plan.

Since the move to SCSS (and to some extent, although not quite as pronounced, with the LESS on-demand processing) fresh page loads have been very slow.

The best 'trick' is the one Emma recommended, simply leave designer mode off and then purge all caches only when you make a development change that may impact the cache (anything building css/js for example)