The Ohr Hachaim brings down that the spies were sarei chamishim (leaders of 50).
Why didn't Moshe send higher ranking officers as spies for such an important mission?
The Ostrovtzer Rav in Me'ir Eynei Chachamim explains that a leader is imbued with the power of the group that he leads, in this case 50 people. He further notes that the Jewish people were blessed that each one of them had the power of a thousand people based upon the pasuk in Haazinu (Devarim 32, 30) (he seems to follow the Ibn Ezra's second peshat). As there were 12 spies, together they represented the force of 600,000 men (12 x 50 x 1000) who were to fight to enter Eretz Yisrael.
Rabbeinu Yosef Bechor Shor (a talmid of Rabbeinu Tam) took a different view. He wrote that they were actually 'sarei alafim' - leaders of thousands.
I haven’t seen much discussion of the Baal Haturim’s opinion that they were ‘sarei chamishim’. However, I don’t think that had they been higher ranked judges that they would necessarily be better spies.
I would like to humbly suggest a few reasons why Moshe might not have sent more senior people. (As a side point, I should probably mention that the Emes LeYaakov held that the spies were chosen through the Urim VeTumim, and if so the question is not on Moshe personally.)
Usually, an army does not send the most senior people on high risk missions. Of course there is a need to send capable people, but not the ‘top brass’. If really the top people should have been sent, why not include Moshe and Aharon themselves?
Outstanding people also attract a greater level of Ayin Hara. This is why we see in the Gemara (Berachot 31b) that when Chana prayed for a son, she asked that he should not be too tall nor too short, neither too thin nor too corpulent, neither too pale nor too red, neither overly clever nor stupid. Therefore it might not be best to send people at the very top.
In addition, we see from various commentaries (e.g. Kli Yakar and the Netziv) that the entire reason for sending the spies was that the Jewish people did not want, or did not feel worthy of a direct connection with Hashem. The level was too high for them. (The Netziv points out that they now knew that Yehoshua would lead them into Israel, and as they had seen in the war with Amalek, the war he fought was on a more physical level.) They wanted to conquer Eretz Yisrael in a more ‘natural’ way. Therefore, the slightly lower spiritual level of the spies would be more in line with the Jews’ request.