Pitching depth seems to be a little undervalued in this league (7 starters v. 12 offense, vs. traditional 9 v. 14), so that makes it closer than usual. I think Johan is more valuable in a vacuum. As well, your offensive replacement (Peralta/Lopez, with LaRoche moving to CI) is a big drop, probably bigger than Buchholz to Johan (but maybe not Zito to Johan). If you stream SP (lineup changes every day, unlimited innings, use all your pitchers every time they start), I'd consider it, but, if you just start the same SP for a week at a time, I'd pass.
With Adam LaRoche finally coming around, as we all expected, albeit a little later than anticipated, I'd probably do this. LaRoche may very well outperform Votto the rest of the season at the CI spot, and then I'd just keep my eyes open for a potential short term impact bat who can fill your Util. slot. Even a guy like Alcides Escobar could help you win SB, etc. -- players like that. I'd probably do this deal.
When I first saw this I was thinkning "Real dumb question" of course you do this trade. Though I looked at the set up and your team and, like the first responder, I don't think you should. Your pitching is strong already, based on it's make up im sure your one of the better pitching teams in your league. I also dont trust LaRoche. I was thinkning moving him to CI and step up Peralta at Util. but I still don't like it. Stick with your guns or get him to up the ante based on what we are saying here. It makes sense.
Is Peralta eligible at 3B in your league? You could slide him into your CI spot. I'd still probably do this deal. There's no assurance that Votto will turn things around anyways.