Return on your seeds

I tend to have a similar thought process with what we grow in the garden, but better taste over the shops is also a big factor for me. I always grow first early potatoes as they taste far better than shop bought. Similarly there is often a few carrots as they are far more carrotty straight out the soil.
Our other staples are broad beans, courgettes, kale, beetroot, globe artichokes, jerusalem artichokes, cut n come again salads, black and red currants, gooseberries and apples. If you count broad beans etc as a good bang for your buck, fruit trees and bushes are another level.

How far apart are you planting your kohl rabi? I grow 4 to a square foot, so six inches apart. They grow quite vertically and don't take up much horizontal space so are good for planting around the edges of beds. I love the crunch of kohl rabi in a salad, good for when radish and turnips aren't around.

I have about  8 plants 8" apart in a row covered in mesh to stop pests, when should they start bulbing? At the rate these are going it'll be winter before they do anything, they're a healthy 10" tall on stalks so far. I still don't think they're going to be a favourite,  I'm not keen on radish or turnip, so there's not a lot of hope for kohl rabi. Good to experiment though.

Maybe just under 2 months from seed to harvest? I've never timed it. Slower than turnips anyway.   You do get the odd one that doesn't form any bulb at all. Hybrid varieties are better than open-pollinated, they bulb quicker and don't go woody.

80% of my veg are in the brassica family, I don't grow tomatoes as I can live without them. I do grow a lot of beetroot.

Never really considered seeds verses return

I love brassicas but trying to keep them pest free during summer sends me loopy. Butterflies and moths are easy enough to keep out with netting, but whitefly and especially mealy cabbage aphid get really annoying.

I agree wholeheartedly about fruit trees and bushes, rhubarb and other perennial vegetables that crop for years being best value plants to grow. If I could only grow one type of plant it would be fruit.
Next would be beans, courgettes, tomatoes etc for productivity (with least effort) per plant. They also get bonus points for being expensive to buy in the shops and are relatively easy to grow.
The roots and brassicas are, to me, luxury crops as I struggle to grow them into anything worth eating. I wish I could!

It's alliums all the way for me! I don't think at any time of the year I don't have some form of allium growing on the plot. Leeks, onions and elephant garlic are my 'go to' veg. It's a little bit of a naughty addition to this thread though as I very rarely grow from seed!  I have also veered away from growing garlic, which gives varying returns. Now I have built up a supply of elephant garlic corms, they very rarely fail to supply the goods.