I kind off think that it is difficult to expand that particular game. However indicating the worth of the cards would probably be helpful for new players to get what they are actually aiming for (e.g. is an Ace a one or higher in value). But if it is about actual mechanics, then either buffs for certain cards would be an idea or a mechanic that allows you to cheat (therefore to observe what cards the opponent has on their hand or to see what cards will be dealt next).