I used the bootcamp and qvault RC tests to help me prepare. I thought bootcamp was the most helpful. You need to find a strategy and stick with it. Doing multiple tests helps you refine your strategy. Time goes by much faster on the real test in my opinion and it's helpful to be able to read quick and take good notes and still be able to answer all the questions correctly.
Yeah resources for the RC section are thin. One thing that a lot of people do are read scientific american articles. These should be similar to the articles that you are going to see on the DAT. I know Bootcamp has some. One thing I have been trying to do is after looking at some of the questions on the limited practice material, I make my own "tests".
I read one article a day (I am still a ways out from my test). I time it and try my best to skim and only take in important information. I then try to think of answers to the questions that I have seen before and try to understand each paragraph while skimming. I then read the article completely and see what I missed or if I misunderstood things.
Not sure if this helps at all for you.
Don't need to practice IMO. The real thing is a lot easier than any practice material out there. If you can read english at a good pace you will do just fine. I took a nap during my RC in the extra 20 minutes I had...
I found Bootcmap, Qvault, and CrackDAT's RC sections to all be pretty helpful practice.