As for mycotrees, they're actually supposed to be giving less food. Bacchus berries take plenty of upkeep, which takes more farmer time. Mycotrees, as an orchard tree, once established will take some watering and a small fertilization effort per year, but ultimately take less farmer upkeep than Bacchus Berries do. Effectively, you can just plant two or three times as many mycotrees for the same amount of dwarven upkeep. (At least, that's the idea behind it... I still have to work on balancing all this.)
Ah, yeah, at the very least you wouldn't have to spend time replanting them each year. If there's more upkeep then that to them, then that's another factor that could be added in the raws, and dealt with in balance.
Actually, this makes me think that I should just write some kind of formula linking these things together to give a ballpark "balance"...
quantity * value = GROWDUR * (nutrient consumption - soil replinishment / 4)
Yeah, it can be good to keep things roughly balanced, just as long as everything doesn't end up being the same, but there seems to be enough factors present with the system here to allow for a good versatility in possible crops too. The two main things you want to avoid happening are having the same one or two plants always used in every situation, or where all the plants are so similar it doesn't matter which you use (and the lesser issue of plants that are never used). Just having the variety of factors that these have, those situations should be less likely to occur.
There's also the question of what factors it's being balanced around. For example, if you're just dealing with farming for survival, the value wouldn't be a particularly useful factor there, and you'd just want to produce as much as possible. Or if you're setting up a fort somewhere really inhospitable, then nutrients and soil factors may be a key factor. Or if you have a really well established fortress, and you want to keep nobles and such happy, then all the value 1 foods in the world won't help you there.
So for example, if you're focusing on survival being a key point, then quantity/GROWDUR might be the major factor. If you want high quality food for nobles and happy dwarves and such, then value of the individual components is of importance over anything else. If you want produce to sell to others, then (quantity*value)/GROWDUR is likely the most important(taking into account soil costs, so something like the listed formula). If you're trying to survive in very inhospitable conditions, then quantity/(nutrient consumption - soil replenishment) might be the key factor. Or if you're trying to grow them in a desert, then quantity/water consumption might be the main factor.
And it doesn't necessarily have to be a linear balance either, plants which excel in some categories might be much worse off in others than what would be expected linearly, as well as other additional effects which can be factored in. Although you don't want to specialize too specifically or obviously. You wouldn't one plant that's always obviously the best for all low water conditions or one that's always the best for x, etc. either. Actually, most of the plants you have so far seems to be doing fairly well in that regard, so just something to keep in mind.
Although, there are enough factors here you could probably just provide a variety of plants with a variety of conditions, and as long as there's not ones that are better in every way than another plant, you'll probably end up with a variety of different plants that are good for different conditions and situations. It wouldn't be too hard to beat the plump helmets or dwarven syrup factory/sunshine choices that currently dominate.
Although I can't even tell if there's much of a difference in growing speed or quantity/time in the current system, simply because it's so easy to produce a giant surplus with a tiny amount of anything that that alone makes it not a major factor. That's something to keep in mind, if it's too easy to produce a large quantity of food, then all those differences between plants cease to matter much, since you could just get enough food by brute force quantity approach.