I'd agree, to a point- handicapped spots are usually closer to the "front" of lot, and thus the door. High traffic area, well lit, everything you want to do reduce your likelihood of being targeted. I would see it as more of a target with a carjacking, park on the street or if you have to use a large parking garage. I guess the only way to answer the question is to sit down with your wife after having your range buddies get you real data, and have a conversation where her disabilities are honestly appraised. Also check with disability advocacy agencies and maybe AARP, they might have the numbers if no one else does. If the advantages of the placard outweigh what I would see as a slight increase in risk, then I would say go for it.

Does Texas use a placard or plates? If it's a placard that hangs from a rearview or on the dash, use it when needed and take it down when you want a slightly lower profile.