How do you determine which coins are worth investigating?
When this altcoin have roadmap clear and promising, you can see it in Bitcointalk ANN thread or homepage Altcoin you want invest
How much time do you spend on average investigating a coin?
Maybe need some days or one weeks to see it good or not, but if want invest long-term 1-3 years, spent more time to find the reason need invest this coin not bad choice
Do you decide wheter to invest following specific criteria or your gut feeling?
Need have target before invest, use feeling just make you have more misstake in future