Sounds something similar to the Vulcan Mind Meld, except forgetting any memories transferred in such a way.

Sanderson had a similar sort of thing in the Mistborn Series where a certain race could store memories, and other traits in metallic objects.

Yours is similar to, but different enough that I think you could pull it off.

Here are a couple of questions that may feed your idea, or kill it if it won't work:

Why do they not have writing, and keep written journals and memoirs? How would it change your magic system if it was introduced?

Why are there memory thieves, who profits from the purchase and sales of someone's great grandparents experiences? Are they primarily employed in espionage positions, hire out like PI's, or mainly stick to inheritance dispute law cases?

What happens to the thief's score if he or she goes blind? Are they now stuck with these epic memories that caused them to lose their sight? Is there any optical correction that keeps them seeing better for longer? Does a retired master thief wear a big thick pair of glasses as a mark of what he can teach young up and coming thieves?

Why does blindness only affect thieves and not keepers?

Is it eye contact only, or eye contact and touch? (I read both above) If it's only eye contact has society developed a habit of never meeting people in the eyes (I sure wouldn't if I might find myself a dotard because my memories were stolen, either that or get a pair of sweet shades to protect my memories)?

In what possible way can someone use this magic in a different way to solve a previously unsolvable problem?