I won't suggest that much but in my opinion, i think the "level up yourself by using your stats" should apply to the base stats only. For example, getting damaged and swinging your weapon at monsters increases muscles, then the stats will scale because of the base stats but the only way to manually increase the stats without increasing the base stats is with the usual juice fountain purchase.
Maybe increase the limits of the stats (currently 19 i think ?) whenever you increase the base stats, like if muscle is increased by 2 results in the limit of the health max to increase by 2 and the health regen by 1 or something. The "items will require certain stats" thing is a good balance for some of the weapons and items, which is nice.
Btw, what is 'Will max' and 'Will regen' ? Is it stats for doing magic perhaps ?