given the relevance to rpi (and thus ncaa seeding), midweek games count the same
however, as stated, the weekend series is when you'll face the best pitching. you'd probably win more midweek games if you threw your best guys then, but you'd lose many more weekend games to compensate.
given the nature of the beast (freshman learning to hit and throw against much better competition) it pays to have some midweek games against lesser opponents -- not many because it kills the rpi, but you need to let them off the leash occasionally or you won't know what you have in a couple years.
i personally like midweek games against teams like arkansas and KSU as well... good teams that help you get better ncaa seeding. it's hard to get a perfect schedule honestly. part of me loves playing cal state fullerton or similar every week. part of me knows a complete grinder could wear your team down. this year is probably a fairly decent balance, especially given that the big ten seems MUCH better in the rpi than they are normally (they're currently 5th in RPI among conferences).