In my experience any source of traffic is worth considering ofcourse content is king but without visitors good content counts for nothing. If you have engaging content then no matter what the source of traffic you will get readers. You mention link exchanges as being a waste of time, some of my most frequent readers have come via mutually beneficial link exchanges between myself and blogs with similar content. Never dismiss any source of traffic or technique that can increase your search engine rankings, my blog regularly appears on the first page of a google search for money making keywords, and thats because I tried lots of different methods of generating traffic and getting links to my blog. It can take a long time to happen though, for the first 6 months of blogging I only made about $40 with adsense and then I stopped blogging altogether for almost year and in that time I earnt almost $400 without writing a single post. I think this was because all the effort I had put in in the beginning was only then starting to pay off, if I had continued posting through that time I could probably made a lot more.
Excellent work though on making that first $50 it can only go up from there, just keep writing quality posts and promoting your blog where ever you can and that figure will just keep on increasing.
Good luck with the future of your blog I hope you make loads of money.