I can say from DM's and the replies on not only my contest page, but maybe more telling are the replies on the pages of the entries from those who were featured that I think they do help.
When someone is starting off on steemit it's just so hard to get noticed and hard to start conversations with people. The contests that are out there allow people to find a niche and engage with other people they may have been afraid to interact with otherwise...or worse their approach may have been viewed as spammy and then they get flagged.
The $$$ rewards tend to be pretty small, but I remember when I first started being excited winning like .35 SBD from a contest and then the next day winning another .25 SD. Back then SBD was under a $1 so the value was nothing, but winning was really cool.
Little things like this helped me stay committed to steemit and convince me to add cash into the system. In turn I have referred a few others who now own steem as an investment and my Brother Inlaw is here blogging...well posted twice now but it's a start. He owns 3000sp due to my recommendation which may not have happened without contests...so do they help, I think so!
RE: Giving Back ~ Does it Help