You do have Kemp coming back next Friday, so there's your help in HR and RBI and SB, plus longo is going to be back soon last I heard so there's even more help in HR and RBIs as well.
I'd say keep Alvarez instead of Zimmerman, but that's your decision. Zim will get you a couple more SB but you take a hit in AVG...
What kinds of names are in your FA or on the WW?
Personally I'd stand pat until you at least get a glimpse at how much longo and kemp help your team first because that's BIG firepower coming back very soon and could be your solution to the rest of your hitting categories
Help with mine? http://www.fantasybaseballcafe.com/forums/viewtopic.php?t=450079