Rebuild or new cartridge with my zeta tonearm

Birdfan, 16 gms seems a little heavy for that arm but I would certainly stay away from cartridges with a compliance over 20 u/mN. If it is indeed 16 gm then you had better stick with the Clearaudio cartridges which are down around 15 u/mN. Most MM cartridges are over 20 u/m. Soundsmith has low compliance cartridges but they are all low output. I assume since you were using a high output moving coil cartridge that you do not have a high gain phono section.

I actually bought schiit’s entry level oh I.. which has all kinds of settings for a range of carts. I believe it will do LOMC. I guess I’ve never been sold on MC as they all seem so expensive.. but I do have preamp

If you were happy with the sound of your Sumiko go for the rebuild it should sound as good if not better than new.
I had my Sumiko BPS Evo 3 rebuilt and was very happy with the results

I very much doubt it will sound better than new.
It will definitely sound different.
It will definitely not sound the same.
It could sound good.
It could sound very good.

 Yes I  Agree with uberwaltz  comment.