I have a real question not some dumb what is a niche question either. I have a site, that is promoting a product and it makes about $100 a week. My question is should I buy another site, same niche and continue marketing it. I know I would be technically drawing away some traffic, but would two sites in one niche make me more money?

My .02 cents:
If I were you I would try to increase the traffic to the existing site. If that doesn't work, then I would try to move to a more profitable niche. You should always be able to scale up.
And in the event you prefer not to scale up your site for X and Y reason, go ahead, make a zillion 100usd/week sites.

I have scaled up I am maximizing profits. If I was to but another .com around another keyword and, use my seo knowledge like the other one would I be cutting myself in the long run?

Probably not, since you would have more chances of trapping a user since you have 2+ different domains which a normal user will assume are not related. Besides, the internet is big enough for you to find a LOT of people willing to sign-up for whatever you are offering on different domains. Just don't make 500 domains .

my bad I wasn't sober when I replied, I meant with a similar keyword, a variant within the niche itself.