I've seen a lot of startups which missed to think about founder vesting in the beginning. One year later the "co-founder" holding 50% decided to travel around the world because "this is way to stressful...". This can cause some serious trouble talking to potential investors.
You are also right! I think if you've build several products before it's more easy to choose the right path building great products. But I do also see a lot of people just building something behind closed doors without thinking about the problem they really want to solve. Of course, justyo.co for example... I don't think there was a huge need in sending YO's :D
Yes, when you've built several products, you definitely start to see things that work and things that do not work and you gain experience. Again, I am not against validation, it just should be used moderately and not exclusively as a key indicator if you should build something or not. Products like justyo.co popup once in a while and due to some pretty random events at some point they become a hype. I tend to think the creators are having a lot of fun as well, without really thinking for monetization that much.
Startups perform best when they focus on making money in one specific way. The model you choose should be based on the economics of the software, for example how much it costs to support additional users.
