I have been playing game for a while now, and I must say if you want to make more than just few farm on your island, building wheat fields is nightmare, I guess many people will agree with me on that. capacity of well is bit better but still considering you need a lot of water for each building it use, is still bit annoying and if you add cost,time spent to build and level requirement, it make it more pain than gain every day, therefore my suggestion is to raise capacity of these structures:
Wells
1000 > 1500
1500 > 3000
2000 (not sure of this one) > 4500
Wheat fields
200 > 1000
400 > 2000
600(not sure of this one) > 3000
As for the costs to build them, think double the cost would be fair enough.
Or instead of changing capacity, make a automatic rebuild on/off option on each field/well, mean once field/well got exhausted it will rebuild it self taking costs of building from your storage without losing level of field/well.
Other thing I think which is must have and will give a reason to upgrade well/field is to not lose level of the build if it is rebuild in exactly same position as it was before.
If you like my ideas please +1 it, as well any input/feedback or additional ideas are more then welcome. Thanks.
Regards
Greg