Bigger is Better - and much more valuable!
Yes, size matters - a lot. Big rugs are rare which of course increases value. Past and present weavers typically weave small to medium size rugs. One reason is limited space. The larger the rug, the larger the loom. Many Navajo live in homes that have low ceilings and low square footage, which makes it nearly impossible for many weavers to take on large rugs.
Another reason weavers tend to weave smaller rugs is the amount of time it takes. Large rugs can take a year or more to complete. Weaver's payday typically comes when they sell their rug. Few can go a year or more without a paycheck. Which means fewer weavers then and now take on large rugs.
Below are historic, contemporary and Churro weavings that are 96" on at least one side.