I notice that a number of tomato plants are growing on their own from which
I assume is last years crop. Would it be worthwhile cultivating them or
would they tend to be lower producers?

Thanks

Tom
They usually produce as well or better than store bought plants. BUT they may
not be what you want. The most abundant volunteers will be cherry tomatoes. If
you only grew regular tomatoes than the volunteers will be similar. Even the
hybrids don't usually segregate much in the second generation.