You'll be banned on digg if you keep digging the same URL over and over again, you need to digg other sites too.
Attract followers who are interested in your products, build a relationship, if your product is good, then you will have a higher conversion rate. You need a lot more followers.
I get a ton of traffic to my sites from Twitter, but no conversions. Most followers are hawking something of their own. You should look closely at who is following you, and you'll find much of the same.
I agree that one of the best ways is to drive Twitter traffic to your own blog posts or forum threads. If they find you content interesting, you will have more blog subscribers or forum members. So in general, Twitter is a great way to build your own community site. And to make money of a community site (especially niche one) is pretty easy: Adsense, relevant affiliate products, etc.
It is important to balance out the number of normal tweets to the number of affiliate of what have you links. The old 80/20 rule works pretty well. You can also tell by mass unfollowing when you try to sell too much