I'd say signature campaigns are a very poor goal now, it's hard to earn merit, and even if you will achieve high enough rank, most new campaigns pay very small amounts like $20-50 per week. Most online jobs pay higher than that and don't require such high amounts of time and effort investment to get started.
This is debatable. If a job barrier to entry is low then it means the payments are not that good. Most online jobs that you can easily register are something like copywriting, ads rating, etc which probably pays around $5/hour or lower than that. You need dedication and time to build your portfolio if you want to increase your salary per hour.
I can tell for sure that a $50/week campaign is good enough for someone from my country and can compete directly with 9 to 5 'beginner' office worker's salary here. That being said, you should not see a sig campaign as a target and your 'main job'.