solid hitting infielders are harder to come by, therefore, i wouldn't trade ramirez. could you offer up butler and young for kemp instead? then you could pick up another 1B or IF off waivers. i'd rather have alexei than derosa honestly, but i don't see how you can trade a starting IF. you don't have a lot of depth there.
seriously though, this is a tough one, your infield isn't great and would hurt if you traded ramirez. but kemp is the better player...
if the waivers has a decent 3b on it, drop hafner for that person, take the trade, and move derosa to second. this will give you a very solid outfield and thus a good player to trade away to plug whatever other holes you have in your roster.
I think you degrade your team with that trade. You don't have a plug in for Ramirez. Unless there is someone on the FA list you can grab with value similar to Alexi you can't do it. Your outfield is solid. Infield positions (as mentioned) are usually tougher to fill.
If you really want Kemp counter with Ramirez and one of your OFs for Kemp and one of his 3bs. That way you can shift DeRosa to 2b. DeRosa is much more valuable at 2b then 3b.
Can you return the favor on my "The Trade Talks from H E Double Hockey Sticks" post plz?