Are the keys in question loose sideways or any other way for that matter ? It is possible that the resting height of the keys might be very slightly different in the middle octaves from use. That will give an appearance of more space between keys or uneven space between keys.
Hire a technician of your choice to appraise the instrument in writing for present mechanical condition, the cost to complete any corrections, and then local market value. All of your questions will be answered. Be prepared to spend a couple of hundred on this task.