The fervor that the picture communicates is in and of itself striking. On the day that Moshe returns to his people, one day after the Torah has been revealed for a second time, he is immediately besieged by throngs of Jews, all waiting on line from dawn to dark for his sagacious words. Some come with questions, some come with disputes and many come to bare their hearts and seek his counsel and prayers (Ramban.)
The same picture evokes Yisro's great concern for his son in law's stamina, as Yisro observes Moshe respond to the questions and travails of every Jewish family with little more than the skeleton crew of Aharon, Chur and seventy elders (Rashi.) "Navol tibol - you will certainly become exhausted, you and those who are with you, as you have over-extended yourself; you cannot do it alone."
One has to wonder why Yisro is worried about the physical capacity of someone who just completed three forty day stints with no sleep, no food and no water! Furthermore, has Yisro not been around long enough to expect that communal curiosity and excitement will eventually abate once Moshe has been home for a little longer?
Perhaps that is why the Rashbam interprets "navol tibol" to say that Moshe may confuse the various questions that the Jews raise and his responses may not be as accurate and as personal as Yisro thinks our people deserve. Perhaps Yisro wants to be assured that every Jew will feel Moshe's "humanness" as he listens to them and responds to them. Yisro might be concerned that Jews will be unsure of the advice they receive from one who brings the super human blessings of his divine encounters to this world, one who never tires and never falters, and they will forever wonder if they can rely on Moshe rabbeinu's judgment.
Yet Yisro's words display fear about the commitment of the Jewish people even as he is troubled by the schedule of his daughter's husband. "Also the people who are with you" is interpreted by Chazal as referring to the little team that Moshe had with him but, as the Ohr Chaim suggests, it can also refer to the Jewish people whose patience is being tested as they stand in long lines for hours and hours. Even Rashi (13:18) sees in Yisro's earlier words that he is bothered that the questioners are not accorded the respect that leadership has to show its constituents.
Thus it seems to me that Yisro is neither worried about Moshe's physical endurance that has been tested time and again, nor about the pressures of a people who within time may have to be inspired to ask respectfully or may well find wisdom among Moshe's students. Rather, Yisro was unsure of a system that did not sustain the passion to ask or the preciousness of inquiry. If there was only one address for questions regarding an entirely new body of knowledge that needed to be understood and applied, or even a few addresses, and those addresses would reasonably be perceived to be overextended, and there were terribly long lines to access them - could questions and clarity really be so important? It would almost seem that we really did not want questions, despite Moshe using all his strength to teach otherwise.
After all, Yisro's driving mission in life included the hot pursuit of questions and curiosities, pursued with rigor and vigor. Indeed Yisro, as Chazal deduce from various references, lived a life of intellectual integrity largely unsatisfied with the "truths" of his milieu. His readiness to sacrifice prestige and position was well proven and it now brought him, and he alone, to our people. Entire nations were awed by krias Yam Suf and countless tasted the runoff waters of the mon, but Yisro alone changed his life to seek "new" truths. He alone may have worried that a religion that would not enthusiastically embrace questioners and their inquiries would not inspire confidence in its teachings and wisdom, would not lead adherents to penetrate its depths, and its depths would not penetrate its adherents.
The joy that undoubtedly surged inside Yisro as he witnessed the dedication of the people to understand was possibly only muted by his anxiousness to maintain that excitement and preserve it for all time. We can well understand the alacrity with which Moshe accepted Yisro's perspective and perhaps that is why to this day students of Torah are often more impressed by an incisive question than an answer of equal insight.