Those are not grilles. You have true divided lights. They cannot be removed effectively as the amount of work would not worth the dollars and or effort.. Replacing the windows is the best bet with Low E Insulated Glass, yours are single pane.

Thanks @millworkman

My aesthetic preferences aside, Thoughts on 1970s wooden windows being better than the replacements would be (as far as function and quality)?
How can I tell if these are good quality windows or not worth saving?

They are fine and with a well sealed storm, perform okay. That said, most storms are far from either airtight or movement accommodating. Before I dumped too much money on these, I'd at least get a number on replacements.

@windows on Washington - thank you for your insight!

My terminology might be wrong, but the frames and sills (interior and exterior) are in good condition (there were storms on most of the windows). There are 2 that need moderate sill work due to rot.

With this info, Would you recommend full replacements or just sash kits?

I would recommend an insert, with capping.