I know there a thousand different products you can make with peanuts. But, my local supermarket has one of these,     I'm wondering if the effect will be similar if I use my mini coffee-bean hand grinder.. You can find a picture of it here,    
You will get the roasty, caramelized flavors; how much influence they will have on the overall flavor of your stew will depend on several factors including:   How deeply you roast the them How much you add, proportionately, into the stew How strongly flavored the other items in the stew are   Roasting the vegetables will also cook them, so you will want to add them to the stew much later, so they don't overcook.  If you google roasted vegetable stew, you will find several recipes for inspiration.  As to whether this is a superior, or heartier flavor, that would be a matter of opinion.  You don't mention roasting celery or onions (partners with carrots in the classic mire poix), but these are also excellent candidates for roasting, as are all types of root vegetable. 