The power these guides offer depends on how thorough of a market search you are forced into conducting when you first start out as a freelance writer. If you run into a market that does not provide enough guideline information -- in a current edition -- if you have older WM edition(s), you can look back to see what the deal is. This can be especially important if you run into a magazine that you believe might be one of the few you are going to be able to break in to.
For example, I discovered a number of incredibly good ideas for children's stories that would fit perfectly within the pages of "Ranger Rick" magazine (National Wildlife Federation).
The WM 2000 CD-ROM listed an editor, but very limited contact info and guidelines (as in NO guidelines):
(Ranger Rick is) "40% freelance written. Monthly magazine for children from ages 7-12, with the greatest concentration in the 7-10 age bracket. *Because of a backup in submissions, the editorial staff at Ranger Rick is not accepting queries or unsolicited manuscripts until further notice."
Ouch! What to do? I looked in in older WMs to see how long Ranger Rick had been having a "backup in submissions." WM 99 listed full writers guidelines and pay-info and well, I'm waiting to see whether Ranger Rick editors like my ideas or if they're going to toss them because of a "backup in submissions." :-)
AND, the '99 edition has added, valuble, useful goodies. Just checked one catagory of magazines, found 6 new ones, 2 dropped from the previous edition. Point: truly up-to-date.
I'd been using the paper version for decades, then told by a writer-friend of the advantages of the CD ROM version. Have it now, and it IS indeed superior!
List price: $39.99 (that's 30% off!)