. One personal disadvantage for us is figuring out how we will afford another year of pre-school....
He is easily frustrated and has perfectionist tendencies which immobilize him. He's stubborn. He's sensitive. (By the way, those last three sentences could also describe me if we simply change the pronoun.)
Thoughts on the endless worksheets and perfectionism: I think handwriting is actually just busywork and repetition and the more you practice, the sooner you get it done, the sooner you can get on with life. Everybody has their own opinions but I think most people don't like handwriting at first and won't like it until they've done it long enough to not think about it anymore. (except unschoolers) Everybody prefers to do things they're already good at. Unless you're going with an unschool or self-paced cirriculum and if you plan to send him to the same school just a year later I don't know that he would like the pile of handwriting homework any better next year.
The main thing for me from your post is that you're straining the budget for the extra year of preschool. I'd rather strain the budget for a family vacation with that money , but you're thinking of holding him back for a year for a reason. Perfectionism isn't immaturity he'll outgrow in a year. With the age difference I think kids treat younger kids a little better even.