However, it would be a shame to put all that money and work into a low end rim.
Very true.
2019 Santa Cruz Hightower CS build. 148 boost. Raceface AR 27 offset rims. Not great but like I said. I will be upgrading them soon. And I can do it piece by piece which is better for me right now.
RF AR rims aren't what I'd consider low end, though. A solid alu rim option. With that said, I think you'll have a hard time selling a DT 370 hub by itself. And if you do, it won't be for much. I think you'll be able to get significantly more for it built as a complete wheel if you want to sell it off. Also worth considering, I bet you'd get more attention for a complete wheelset, too.
You WILL need new spokes for a rebuild, there's no question there. Besides, I bet your stock wheels don't use particularly fancy spokes, either.
IMO, if you're going to spring for hubs as nice as I9, you owe it to yourself to build them into a wheel that YOU want from the ground up, designed around your riding style and terrain.
IIRC, you can upgrade the ratchet mechanism in the DT 370's. I'd do that for the meantime (it will probably help the resale value of those wheels later, too) and then replenish the bank account for the wheel build that I want, rather than doing it piecemeal.