If your wife wants a 300 gal fowlr tell her to go buy one and you set up the tank that you buy the way that you want it. Honestly the price between a fowlr and a reef should only differ in the cost of corals and nutrients. from what i understand if ur keeping LR u need the lights anyway and you need reef type filtration anyway. No reason you cant keep the eel, a niger, and a lion fish in a reef tank. just watch ur hands when ur servicing the tank.
is the conflict centered around what type of fish u want in the tank or is it about the corals? personally id go with a nice school of anthias, some pretty tangs, tons of inverts, maybe a dwarf angel, some spiny urchins and bangai cardinals, and clownfish/anenomes and see how many different symbiotic relationships I could maintain in 1 tank... or go with an aggresive reef with aforementioned fish but maybe add a banded cat shark (love those guys) or a wards wobbegong ( i know a guy who can get them regularly, and they only grow about 30 inches and are so lethargic that people have kept them in captivity for their entire lives in 135 gallon tanks). You could do an octopus or cuttlefish set up that would be bada$$. Mimmic octopus in a tank that big would rock cus ud prolly be able to see some of the mimmicking behavior.
At the end of the day u both have to live under the same roof, and its not really worth fighting over, but at the same time compromising sucks and usually a compromise is a resolution to a conflict in which neither party gets what they want so whats the point? but if youre gonan try to compromise i say wobbegong/ aggressive reef ftw!!!