hi...just my opinion but I would think kitty is lacking something in this diet, his system needs something he isn't getting therefore he is constantly trying to achieve it....with my cats when they are on a good balanced diet they eat very little, my 13lb sami eats no more than a few tablespoons a day of canned(now raw mix)..and perhaps at the most a 1/4 cup of dry....he never begs.
my nemo won't eat anything except his one brand of dry food, again abt 1/4 daily...but he munches all day just a few bites each time...and he is constantly asking for treats from the table....he loves peanut butter and butter alone...so I'm thinking he needs more oil in his diet and he's satisfied with those.
good luck...talk to you're vet abt adding something with his diet ie: omega 3's?
For starters, I'd suggest trying the expert forum.
But It could be a diet issue, but it sounds like a compulsive eating habit your cat developed over time.
The vomiting could be a separate issue.
I've had success with some cats moving them onto a less expensive, low ash diet with crystals and taking them off dry food (only some, mind you).
However, I'll point out that there is dispute over the idea ash content causes crystals.
I'd definitely consult a vet about some other food options if your cat is vomiting frequently, though.
Be sure to keep the portions VERY small, as if kitty is gorging and bolting it could cause vomiting.