See the "Controlling the Script and name" part of this SO answer. Once you setup your userscript as directed there, then you merely save your changed script file and hit one "Reload" link to update it in Chrome. It's much nicer than the drag and triple-click method, although you'll want to keep the extensions tab open for lots of rapid changes.
Alas, Chrome may never make it easier than that. I can't find it right now, but pretty sure I once saw a discussion where they didn't want to check extension/content-script source for updates on every page load. It would needlessly slow Chrome 99% of the time.