"they were not the be-all and end-all as far as influence on the whole field"

You CANNOT point to one album or one group as the SINGLE be-all and end-all. If there were such a beast, then all the music would sound the same - which it clearly does not.    The Kingston Trio have been sited as being the group as having the most impact on opening peoples ears to folk music, and if you are looking solely at numbers, then that is clearly true. More people became inquisitive about folk music after hearing "Tom Dooley" than any other single recording. That doesn't mean they only listened to the Kingston Trio.

I may drift into a restaurant because I catch the smell of pizza, but once I get inside and look at the menu, perhaps I will enjoy a nice pasta dish or chicken parm and never touch the pizza. The same thing can be said for folk music.   I think if ANYONE relied soley on ONE influence, then they are going to lack any sort of depth and will miss out on an opportunity to evaluate the music in comparison with others.   Bob Dylan has cited influences including Hank Williams, Odetta and Woody Guthrie and he developed his own style from it.

Much earlier in this thread, someone mentioned that people tend to disregard sources other than those that they know. (I'm paraphrasing).

The "folk revival" did not start in the 1950's. You can go back to the start of the 20th century when people like John Lomax began publishing his collections, or perhaps even further back with the work of Francis Child and others. Cecil Sharp had a huge impact. The folk revival that started then was not focused solely on music. It became important to many people(and I'm speaking primarily of the United States but it is certainly relevant in other countries as well)to preserve "folk" traditions as technology began advancing and changing our culture. Perhaps Carl Sanburg's "American Songbag" collection had a far greater impact than we give credit to.

Beginning in the 1920's, commercial recordings of "ethnic" music found a market. These recordings, which Harry Smith used to create his collection, probably had a greater impact on preserving folklore. Perhaps the Carter Family were the most successful, but think of all the hundreds of artists and songs that were saved and later sung.

Folk Festivals began cropping up in this country during the 1930's, and although their approach was different that what we have today, they were a huge influence.

When you give credit to the Kingston Trio, can we forget about Frank Profitt? Frank shared the song that was part of his families heritage with Frank and Anne Warner.   Frank began performing it in his performances.   Roger Sprung, Erik Darling and a group of musicians would then record the song for a small record label. The Kingston Trio heard THAT recording, made very slight revisions, and had a huge hit.   Who was the most influential in this case?

You will sooner come up with a definitive definition of what folk music is before you come up with the definitive or "most influential" album.   I think all of the suggestions above have played an important part in the CONTINUING folk revival and none can be dismissed.