Using options in stat screens

This might not work through the stat screen, if I understand this comment correctly. You can’t set variables through the stat screen. Try to create a separate file for setting gauntlet powers and use *gosub_scene when changing is needed.
Edit: Added an example how that might work:

*label this_action
*choice
	#Before I do anything, I'll change my superpower.
		*gosub_scene power_gauntlet select_powers
		*goto this_action
	*if (power = "Super strength") #Attack the enemy with your super strength!
		You punch the enemy!
		*goto next_action
	*if (power = "Super speed") #Dodge the enemy!
		*if speed >= 60
			You dodge successfully!
			*goto next_action
		*else
			You can't dodge completely!
			*goto next_action

If you choose the 1st option, you are taken to label select_powers in the power_gauntlet file you hypothetically created.

*label select_powers
Do you want to change your power?
*choice
	*selectable_if (power != "Super speed") #Use super speed.
		*set power "Super speed"
		*goto select_powers
	*selectable_if (power != "Super strength") #Use super strength.
		*set power "Super strength"
		*goto select_powers
	#Return to the game.
		*return

You can try this.
I’ve also taken a look at your label beginning. It won’t work for what you are trying to do.

The problem

You are using *input_text command for numerical variables. If you input 100, the game won’t treat it as a number 100 which can pass *if speed >= 60 condition, if will treat it as a text which reads “100” and can’t pass.
Use *input_number instead. And, unless you want to allow players to play on god mode, set up a limit of points you can allocate to your stats. I’ve written an example code for you:

*temp max_points 100
*temp points 0
*label beginning
You have ${max_points} power points left. Allocate them wisely!
*choice
	#How strong are you?
		*input_number points 0 max_points
		*set physical +points
		*set max_points -points
		*set points 0
		*goto beginning
	#How fast are you?
		*input_number points 0 max_points
		*set speed +points
		*set max_points -points
		*set points 0
		*goto beginning
	#I changed my mind! Let's re-allocate the points!
		*set max_points 100
		*set points 0
		*set physical 0
		*set speed 0
		*goto beginning
	#I've finished!
		*goto next_label
*label next_label