I was talking to a vineyard manager here in Niagara who likes Japanese beetles. They generally emerge about the same time that we need to hedge and they only really feed on the new young growth at the top of the canopy, so they basically do the hedging for you and save you the work. Sure, the vineyard looks like crap for about two weeks and you would swear that serious damage has been done, but things recover and the beetles are not an issue for the rest of the season.
I'm sure that this guy's opinion is not shared by most other growers in the area, but I thought he had an interesting point and one worth considering. I think that too often we see some bugs on our vines and some feeding damage and we think that the only rational answer is to wipe them out, but there may other solutions.
In regards to Sevin, don't kid yourself about the toxicity... it may not be the worst out there, but it's a carbamate and they are pretty serious chemicals. As long as you wear protective gear when you're applying it and you wash up good when you're finished, it'll be fine, but it's not something you want to be too complacent about. Repeated exposure can be particularly problematic... it is basically a nerve poison. It is also highly toxic to bees which is not good. Google the MSDS for Sevin if you want more detailed info.