Pancakes, grilled cheese, quesadillas, hashbrowns, fried eggs, bacon, steaks, chicken, pork chops, sauting veggies, fried rice and a hundred other things are perfectly achievable with a stove top griddle. Especially if your stove top is oriented such that you can lay the griddle sideways rather than back to front.
Likewise cast iron holds heat well, and distributes it evenly so less hot/cold spots due to less than optimal burner placement.
Preheat the heck out of your cast iron griddle, be aware of where your burners are for hot/cold spots, and have the right spatulas and you're perfectly adequately prepared to handle most anything.
If you do find yourself doing a LOT of gridding, go ahead and pursue a dedicated griddle. I was given one as a birthday present Sept of last year... took me until July to actually need it.
Just consider your need before buying a dedicated griddle. Not knowing your need, jumping right into one could be really poor advice.