States don't represent the distinctions in culture that they once did. Most people don't know why North and South Carolina are two states, and those who do likely don't share the same concerns as our ancestors. Frankly, the boundaries between all states suffer this problem to a major degree and could use a rethink.
I'm not sure if I care about the number of states, because I'd like to see some major changes in the federal legislative branch:
Regions I'd like to create a few federal regions which represent cultural areas of the US. Most federal laws (except things like declarations of war) would start in the regions, and laws could be distinguished to target urban vs. rural areas. These regions and urban/rural subdivisions would become the "laboratories of democracy" that states have failed to be. Regions may adopt and tweak laws from each other, and any law adopted by two or more regions could be eligible for nationwide consideration (by full vote).
House of Representatives Districts would be larger, bounded by region lines instead of state lines, and each region would have multiple winners. For example, each district could have 2 winners or each could have 3, so that 51-49 ties don't leave half the population without representation.
Senate Each state would be reduced to one senator, appointed as a representative of the state government. Additionally, each region would hold a popular vote to elect one senator from the urban population and one senator from the rural population. Finally, each Senate committee would have two members, chair and co-chair, voted in by national popular vote (the remaining members would serve on these committees as they do today).
All laws would require 60% vote to pass, either regionally or in nationwide votes. Regional laws would be voted by members from the region (in the senate, regional votes would include senators from the states in the region). Senate committees have the power to bring to the floor laws which are proposed to all regions, and the committees would attempt to reconcile the differences between similar regional bills and existing regional laws.