a worthwhile trade-off

Rashi comments on "shelach lecha" that Hashem told Moshe that he already said that Eretz Yisrael is a fantastic country and no more should be needed, but if the people demand spies and Moshe wants to send them, then the choice is his.  

It seems from Rashi that the sending of spies shows a lack of bitachon.  Ramban asks: if that is the case, then not only are the people guilty of not trusting Hashem's promise, but Moshe is guilty as well, as in Parshas Devarim the Torah tells us that he also thought sending spies was a good idea, "va'yitav b'einay ha'davar."

Ramban answers:

ויתכן, כי משה בעבור שידע כי היא שמנה וטובה, כמו שנאמר לו: אל ארץ טובה ורחבה וגו׳ (שמות ג׳:ח׳), בעבור כן אמר להם שיתנו לב לדעת כן, כדי שיגידו לעם וישמחו ויחליפו כח לעלות שם בשמחה.

Moshe did trust that the land was good and fantastic, exactly as Hashem said.  That belief in Hashem's promise is precisely why he thought sending the spies was a good idea -- let the people see for themselves just how good Hashem is going to make it for them, and then they will be happy and excited to enter the land.

R' Zilberstein (in NIfleosecha Asicha) points out that we see from this Ramban the tremendous importance of doing a mitzvah b'simcha and with hislahavus.  Even if sending the spies showed a lower level of bitachon, even if it carried with it certain risks, the net result of being able to fulfill the mitzvah of yishuv ha'aretz with greater joy made it a worthwhile trade-off.