The ansaw is in your question right steering at you.
spined them to death only changing the keyword(niche)
Just doing this on a main website tell Google to say goodbye.(called spam)
it only bring 150-200 UV daily
who wants to read spam, your trying to get one article and spin it hard, to make 400 articles, but it all the same article just spun that=spam.
investing in quality articles
just start again, and invest in quality articles, with long tail keywords, for traffic and sales.
There a art in getting money online , it all about reading and learning then take action.
Domain name needed, prefebaly a exspired domain of choice in your niche with high DA 30 or over metrics and over 20 TF trust flow.
Then a host around what $5 per month.
Join Google then join google adsense then join paypal then join adwords and also join YouTube and then Facebook,twitter.
Know design a nice web site, with your niche in mind,add video and add images and write good strong content with long tail keywords.
also add some niche selling product usually clickbank.
Add the terms and condition and any declaimers and any legal pages with statements on (all links to protect you and the public.)
Create all your social media accounts, and advertise your website on all accounts point one link to your website.(Laser traffic from social media accounts.)
Know create a main blog that explains your website, but with long tail keywords also, also add adsense from Google to generate more cash.
also add one link pointing to your website.
(This main blog is a tear 1)
know write loads of blogs that are all longtail keyword, around your main website niche.
Point all links to the main blog only.(This is tear 2 blogs no matter how many you create.)
know go and get a fresh list niche related,of 100.000.00 links for gsa ranker to post to all them blogs on tear 2 only.
That it ,watch the stats and income from your website.
Good luck bro.