I'm transitioning DD to cow's milk atm, she's down to half & half formula/cow's milk but I still have a brand new tin of formula to use so will be a while before she is having straight cow's milk.
IMO the toddler formula's are a waste of money, and really just a marketing ploy on the part of formula companies. If you do find your DD isn't taking well to the cow's milk then I'd think about it, but I would try transitioning onto cow's milk first. FWIW DD is still having the step 1 formula, her body just couldn't cope with the Step 2 formula, so I think the "extra's" are just for marketing purposes...
You can still leave her on the formula she is on for a little while longer, it won't hurt her either way.