Here's an idea...
They could keep just the bullens only, and with it the link to all the history. Remove the cladding and restore the original brick on the road side.
Inside, the lower bullens section can be removed and the paddock can be reprofiled so that the back row is the height of the lower bullens is now, but a couple of metres further forward. This will make the views better, which is important if they want to get more through the turnstiles for the women's games. Then, that entire underneath bit could be a nice open concourse area that overlooks the pitch which you can access the paddock from. Guessing it'll be about 4k seats. The upper can be pretty much mothballed as it is, and can be opened up when needed for high demand games, such as the derby.
At the park and street end, build a block of affordable apartments that top out at the same height as the bullens, so the feel of the stadium is preserved. You could add a small bank of terracing at the front of each perhaps.
You could make a great feature of the church on the main stand side, opening it up in full to the ground. You could place community use facilities here, with a glass facade that overlooks the pitch. Changing rooms etc can be added here as well.
I think this would look great, maintain the most historic stand and provide a great venue going forward