LB, if there is a good chance that a frum family would buy the house (I think 50% is a good chance, considering the actual % of frum Jews there are in the general population) then you should make the kitchen kosher user-friendly. It sounds like from what CTL was saying, that non-Jews would appreciate 2 sinks also, so if you have the room for 2 sinks, go for it. But keep in mind that having side-by side double sinks is not as convenient as having totally separate sinks in separate areas, if that is technically possible.
I know from the seller’s point of view, fixing up can increase the value and sale-ability of the home, and that you usually earn back way more than was invested in the renovations, but from the buyer’s point of view, I rather put in a new kitchen that fits my taste and needs, and is built of a quality to last, rather than pay more for the house because it is renovated and get a kitchen that may look nice but does not fit my personal needs. For example, I want place for 2 ovens, and an extra freezer, and don’t like to have to walk around an island to get from the counter to the oven, while a different buyer might really want that barn sink in the island. So maybe by not renovating, you increase the sale-ability of the home?