This is depending your effort and times to spend to do task of bounty, if you want to get reward more than $1000 amonth you should be join many different bounty and did it by 8 hours aday or more. But there are also small risk when our work do not approved by bounty manager, so its better we do combination of bounty and trading as well, so we have 2 different income.
Wow it would be really huge if someone is actually getting $1K a month doing bounty. But 8 hours a day? All of you have is sit in front of your computer and tweeting and RT and Facebook link? I don't think I can do that.
Most of the project are worthy and paying while most are not worthy and paying it all just depends on the team behind it so definitely you can't know which project will be successful and not successful you just have to participate and hope it will be successful.
Why do you hope it will be successful? What don't you do your due diligence and study the project before joining so that you will not be scam at the end? Yes, we don't know ahead of time which project will turn out to be scam, but at least if you do your homework and study the ICO before joining then most likely you won't just join any bounty and "hope" that you will be paid in the end.