Dale Carnegie writes that people are motivated by 2 things. Fear and money. What Az is suggesting (some may call it bribery, some may call it “mezumin” – doesnt the Rebbes Gabbai get a few bucks for his “effort”, call it what you like). You want the shadchan to work harder for you, give him or her something they appreciate. Money is pretty univesally appreciated. Whether this is a solution to any so called crisis is a seperate question.
I suspect, that when this “appreciation” is seen as a means to get shadchanim working for a particular person everyone will do it. Then we will have a new “crisis”, people will no longer be able to afford to show their appreciation as desperate parents, driven by an (not so?) irrational fear that their daughters (sons) will remain single forever, try to outdo each other in their displays of “hakaras hatov”. I would even go so far as to suggest that the shadchannim who accept the largest displays of hakaras hatov will be see as the “Lexus” of shadchanim, after all, you get what you pay for, resulting in shadchannim who simply dont have enough time for everyone (wait, isnt that where we are now?). Soon, people will see this as a lucrative field, and the quality of shadchanim will become so watered down, people will stop using them altogether, or go to a select few (again, back to where we are right now). When that happens, some “askanim” will try to create new “hakaras hatov” guidelines. Meanwhile, the only people who gained anything, are a select few shadchanim and a few couples who they managed to set up.