if we were to approach a neighbouring hotel and try to negotiate an arrangement for meals?
I think you will find that as a general rule of thumb it is perfectly OK to dine in Hotel Restaurants, and you simply pay as you would in any other Restaurant. This is why most Hotels ask you to show them your Hotel Room Keycard or some other form of identification on the first few occasions you enter the Dining Room, (until the staff become familair with your faces and then this is not necessary) as as a Guest you clearly do not have to pay as you have paid in advance with your booking, but as a Non Resident you will need to pay of course.
We have done this in Benidorm on a few occasions. I've seen many Hotels where a Menu and Tariff is clearly displayed somewhere on the outside. Just look for a 'Non Residents Welcome' sign.
The only exception to this would probably be at Christmas and New year Gala Meals where you may have to book a table in advance.