You don't need a tractor. Tilling the land will kill off beneficial organisms like earthworms. A better strategy would be to cover the land in tarps until the existing plant life dies, then add 6 inches of compost to areas you're going to sow plants.
This takes a lot of waiting for the plants to die and a lot of money for the compost, but it should produce better results in the long run.
Maybe not to till the land every year (agreed about your comment of the beneficial organisms), but to do miscellaneous tasks, they are incredibly handy. For instance, in my area, the land is famous for "growing rocks". If you had an acre or two you were going to do any long term farming, the first thing to do is clear all the fist to breadbox size rocks. This is sooooo much easier with a tractor and pull behind trailer, or front end loader. Digging holes, moving dirt, and carting finished produce are also things that a small tractor is very useful for. Is it absolutely necessary? No, but unless farming is the full time occupation, it is very nice for a small 1-2 person operation to have.
But clearing the field in the most fun part of starting a new game of Harvest Moon! (:P)
Yeah I can imagine at least having a truck to cart away all those rocks would be pretty handy. But once you're established you won't have to do it again, right? Could just rent it when you need it.
This takes a lot of waiting for the plants to die and a lot of money for the compost, but it should produce better results in the long run.