i'd be careful with universal thresholds like x clicks or x impressions.
30 clicks on a cheap lead offer and 30 clicks on a high-payout funnel tell you very different amounts.
for me the better question is whether the data is enough to make a decision at the level you're optimizing — creative, source, placement, geo, etc. sometimes the overall campaign looks mediocre while one source already has enough data to clearly keep or kill.