I think we are going with 24" beds on 36" centers for most of the garden. I'm thinking 30" might be better than 24, but the Mrs. wants 24 as they are not so far to bend over to weed.
We are not using any plastic mulch. I'd like to get things figured out to do with out it. We are going to drip watering this year however. Last half of last summer was very dry and hot, making it a challenge to keep things watered. We will also cut the amount of water needed with the drip lines. Another expected bonus is that we will not be watering as many weeds this way, either!
We were given some used row cloth cover last spring, and planted 2 identical rows side by side, one which we covered. After 3 weeks, the covered row was about 1.5 times as high as the uncovered row, when we took the cover off and put it on the tomatoes. By the end of the season, I could not tell the difference between the rows, except that the parsnips we harvested were still about 1.5 times larger. When I stuck my hand under the cloth, the ground was noticeable warmer. We are planning to cover most of our rows this year at the beginning to give all the plants a better start. We ended up with the best crop of tomatoes we have had yet, btw, and the earliest off the vine as well. We are in a cool climate with a fair amount of morning and evening shade on the garden. We average about 19 days over 80 degrees in the summer.