The focus on the DAT is what it is. Comprehending what you read and recalling, hence strategies like Search and Destroy and Mapping, with some tone questions. The MCAT is much more difficult because it's essentially deep tone questions, asking things like "which of these is the author most likely to agree with," "what would be a reasonable conclusion," etc.
So if you want, go for it, just keep in mind they are in no way exemplar of what you'll find on the DAT. I scored a 23 on RC and never got higher than a 10 in VR on the MCAT =/
However if you're going to do it just to improve speed, likely reading anything will accomplish that much.
Totally different. To prepare use a reliable science website with studies - NIH is cool...ACS or SciAm (although that's pretty controversial but there's a nice selection of articles).
NO. As stated MCAT tests inferences, meanings the author intends, what the author would think about something unrelated to the story, etc.
DAT tests things like direct facts from the story, summarizing the main idea, and the meaning a word from the story.
I took the MCAT, got a 9 on VR. Took the DAT with no practice, got a 22 on RC.
THE BEST PRACTICE for the RC section is to get DAT RC sections from topscore, achiever, practice exams, kaplan, etc. ANYTHING that is a DAT practice exam RC is how to study. Reading large amounts of science literature/magazine's will not help at all.