Moses sent out spies, but so did Joshua.
Here's the difference:
Moses sent out spies out of a lack of faith - they did it out of curiosity to see what the land looked like.
They were putting their toes in the water to see if they wanted to jump in.
They weren't in a battle-ready mindset.
Joshua sent out spies based upon faith - He was getting ready to attack Jericho and he was mapping out his attack.
They were going to jump into the water, even though they didn't know how yet (Joshua 1:2).
He wasn't going to wait for steps B-Z before he moved - he already had step A, and that was to simply GO!
Joshua was battle-ready.
This is how you can have two Christians "doing" the same thing, but one of them being motivated by fear and the other motivated by faith. You won't be able to tell the difference between the two until conflict arises. Only then will you be able to distinguish the warrior from the wimp.
This is why he only sent 2 spies - he learned that the more that went the more likely they were to fear the people of Jericho.
Joshua was going to take the place God had granted him - they were just spying out their route.
Joshua 5:15 - God shows up to Joshua and says the same thing He said to Moses - "Take your shoes off."
Essentially He was saying, "You wanna lead my people? Treat Me as Holy. Be reverent toward Me."
Good leadership is good followship - Who are you following and how are you following Him?
The test of Joshua's leadership came when God gave Him a "crazy" plan, just like He did Noah.
He told him to march around Jericho with the priests in worship to the Lord.
Out of reverence Joshua obeyed His leader and he became a great leader - the people followed.