Return on your seeds

Although I've never analysed why I grow what I grow, I totally understand and agree with that rationale. Bang for your buck is definitely a reason, as is likelihood of success and taste.
You have to add in the faff factor of growing, whether you actually like the veg and the cost of buying instead of growing. This year I'm growing Kohl Rabi merely because I was given some plants, I'm not yet totally convinced they're worth the space and probably wont be growing it again. Now sweetcorn, that's a different story. On the downside they take up huge amount of space, you're lucky if you get more than one cob a plant but the taste is to die for. As for tomatoes, beans and courgettes curiosity plays an important part, the new variety might be so good that all others are unnecessary