If you are replanting that field with pumpkins rather than rotating to another crop, you could have some problems. I personally don't like to contend with volunteers. I f you only had one kind ( cultivar) in the area and it was open pollinated the you will only have to contend with excess plants. If hybrids or they got cross pollinated, the volunteers may be inferior or at least different from your regular crop. A major problem that can arise with not rotating is disease buildup. That said the tilled in pumpkins will add nutrients and organic matter to your soil.

The field that got the pumpkins was from my manure guys horse farm where they had a big party that donated all different kinds of pumpkins and gourds.
So he dropped off 30 yards of manure with all these pumpkins in it so it was left there for me to deal with. So I just spread out the manure and the pumpkins. There was nothing planted last year at that spot.