Most of what drives people to grind is the sense of progression, and in that regard, the "resolution" or the "ending" part of the game is postponed as much as possible. So much so that the grandest of finales pale considering the grinding hours.
So I think the best way to improve the grinding-based games is focusing on what comes with grinding and make it grand instead. I think the best example will be minecraft. No matter how much minerals you mine, how many woods you chop, you will always be able to make something grander with them. As four friends, we have worked day and night, in shifts, under the ground digging lots and lots of minerals and chopping woods over woods and built ourselves the grandest of castles with everything in it. It had an observatory, library, barracks, prison, courtyard, throne room, kitchens, bathrooms, towers, ballistae, hidden passages... yet still there was room for improvement. Even if worked a year and made our castle perfect, then we could still build a town around it. It's endless, so the grind taking forever is meaningful now.
Though as it happens people generally use construction mode or cheats to get the resources neccessary, but played in our way, it was actually a fun grind, and the result was much more sweeter.