It's your decision as what you do with the information you get on this forum. You will get those who are direct and have seen so many ideas similar and are quick to gun you down. There are those who will give you a glimmer of hope with a supportive suggestion. Then there are those who will give you a bit of both. It's all perspective so my advice would be to look at business ideas from different perspectives as you may find something positive in them all.
My 2p on this would be in the experience of someone who posts on job boards all day. Do your research. The path has been walked so many times and there are those who've just done extremely well with the backing of financial powerhouses to bolster their marketing clout. However there is a little bit of room left for those kind of niche services.
For example, travel website, dating website etc... There are literally thousands out there offering the same thing just in different ways. However that didn't stop someone from stepping it up with a "Premium" service. The challenge will be encouraging the source of jobs to appear on your website. So if you can get your research done and your network is big enough full of recruiters you might just get something going here....
For example travel has "Luxury" holiday providers... they knew the market was saturated with rich buggers so they only targeted a niche area of the market where they could charge the big bucks.
Then there's the dating industry, again millions of different scatter gun services. Then appeared the "Elite" dating and the "Professional" people dating services... Nailed it right?
So from someone who is in the game you're targeting my advice would be to grow your network on Linkedin full of recruitment consultants as many as you can get over a few months to a year. In the meantime build that kick ass premium service for the high salary roles? You may be surprised with the success of such an idea
I want a credit or a glorified section just for me if you make it haha!
Good luck buddy!