I think the plot sizes right now are limiting. Yes, you can merge them but there is also a merge limit. that also doesn't account for smaller plots under 111x111 blocks.
Some plot sizes:
16x16 A chunk would be nice for mini build competitions and also let people do smaller builds and still make it look like something.
75x75 Again this could be good for mini build competitions and smaller builds.
111x111 This is a good plot size, and it should be kept.
225x225 Again this is a good plot size.
501x501 Yes this is big, but it will also allow for larger builds that will increase people's imagination for enormous builds.
Note: all these plots will be bought with different amounts of mana.
Some plot sizes:
16x16 A chunk would be nice for mini build competitions and also let people do smaller builds and still make it look like something.
75x75 Again this could be good for mini build competitions and smaller builds.
111x111 This is a good plot size, and it should be kept.
225x225 Again this is a good plot size.
501x501 Yes this is big, but it will also allow for larger builds that will increase people's imagination for enormous builds.
Note: all these plots will be bought with different amounts of mana.