The key to making money in IM is not necessarily just traffic, but targeted traffic - simply put, traffic that converts.
To answer your question about whether or not it is worth it to switch from mass market to niche, the answer is no....don't switch. Instead, build on this method that you have - especially if it generates a fair amount of broad based traffic. Once they get to your pages, send them to more focused pages on those individual niches.
If your site gets broad search term traffic from Google for sports, cars, and whatever else, then begin to develop niche sites related to each of these topics such as Fantasy Football, baseball, soccer or exotic cars, family wagons, etc. You get the point.
It really boils down to how much work you are willing to put into this marketing method and the returns that you are looking for. You sound as if you would like to re-think your strategy because you are not satisfied with your results thus far.
My personal recommendation would to not necessarily abandon the 'mass market' approach, but to successfully incorporate niche marketing methods with it. It will require the same efforts, as you have done with the mass approach site, to build niche sites as article writing, SEO, etc. are the same....it's just the content that is different and perhaps your sites' design. Cost could be higher as more domains would probably need to be purchased because sub-domains just look too messy and unprofessional (leading to lower conversion).
Conversion is the key to successful internet marketing. Targeted traffic is more likely to click on your offers or even just your Adsense ads in hopes of finding further information on a subject. Drive 100,000 people to a mass info site and receive 50 clicks or drive 1000 targeted people to a 100 different niche sites with 50 clicks each...your choice ultimately but I know which tactic I would prefer.
It also depends on what method you are using to monetize your site. It sounds like Adsense is your focus here but I could be wrong. Lots of traffic is good but it's what you intend to do with that traffic that matters. Mass Information sites actually can do well here if they are set up correctly and are based on highly coveted search terms(i.e. - insurance, medical, health, finance, etc.) as the CPC rates can really add up with just a few clicks. Mass affiliate review sites work well too if they are set up correctly by capturing leads with e-mail opt-ins, etc.
Using what you have already built with the mass marketing approach and linking to various niche sites from there is a good idea. From those niche sites, you can experiment with several different monetizing strategies as a test and then figure out what works best for you.
Good luck with your project!
