Why didn't Moshe daven for Kalev as well?While very creative and while it conveys a nice homiletic message about bechira and tefillah, I wonder if it truly reflects the intent of Chazal in their midrash. Even if not, it can be a nice neo-midrash, with value in its own right.
Rav Elyashiv in Divrei Aggada answers that Yehoshua was Moshe's talmid and there was no doubt that he would stay in his tzidkus no matter the circumstances. All the Meraglim knew this. Moshe was afraid that if things turned sour like they in fact did, Yehoshua's life would be in jeopardy because the Meraglim may want to kill him since Yehoshua would outwardly take a stand against his peers. For this Moshe davened that Yehoshua would remain safe and unharmed.
Kalev on the other hand took a covert approach. He would appear to agree with the Meraglim until he arrived safely back to the Midbar. Because of this he was not concerned with his physical safety. He was more concerned that by outwardly going along with the Meraglim it may influence his "Pnimiyus", his inner soul and he would end up just like them.
But what gives me pause is a few things. Firstly, the midrash rabba on Shelach states that indeed Calev did oppose them physically:
Of course, Bamidbar Rabba is a late midrash, so this, too, may not reflect Chazal's intent.וַיָּבֹאוּ עַד-נַחַל אֶשְׁכֹּל - לא רצו לטל מפרות ארץ ישראל. אלולי כלב ששלף את הזין וירץ לפניהם ואמר להם אם אין אתם נוטלים או אתם הורגים אותי או אני הורג אתכם, לא היו נוטלים. אִם-לֹא הָאָרֶץ אֲשֶׁר דָּרְכָה רַגְלְךָ בָּהּ, לְךָ תִהְיֶה"And they came unto the valley of Eshcol" - they did not wish to take from the fruits of the land of Israel. Had not Caleb unsheathed his sword and ran in front of them and said to them, 'If you do not take (the fruits to show to the Israelites), either you will kill me or I will kill you,' they would not have taken. (Then it cites the verse from Yehoshua, '...Surely the land whereon thy foot hath trodden shall be ___ to thee..."
But the gemara in Sotah 34b juxtaposes the two of them and calls both to be "delivered from the plan of the spies," with no hint of a distinction in how they would respectively fall to the plan of the spies. And the gemara treats them as equal, by asking why Yehoshua would not have to pray while Calev would. This interpretation just does not feel right.
Finally, Rashi interprets it in accordance with what seems to be its true meaning. To be delivered from the plan of the spies means not to be enticed into joining into their counsel and secret evil plan. Thus, Rashi writes regarding Calev:
|and he came to Hebron: Caleb went there alone [hence the singular “he came”] to prostrate himself on the graves of the patriarchs [in prayer] that he not be enticed by his colleagues to be part of their counsel. Thus, it says, “I will give him [Caleb] the land on which he has walked” (Deut. 1:36), and it is written, “They gave Hebron to Caleb” (Jud. 1:20). - [Sotah 34b]||ויבא עד חברון: כלב לבדו הלך שם ונשתטח על קברי אבות, שלא יהא ניסת לחבריו להיות בעצתם, וכן הוא אומר (דברים א, לו) ולו אתן את הארץ אשר דרך בה, וכתיב (שופטים א, כ) ויתנו לכלב את חברון:|
I would add that this interpretation of Calev remaining silent and making himself appear as if he were part of the plan finds purchase in pasuk 30, where he quiets the people with a question that seems as if he is going to join the attack.