We have used Singapore Math from EarlyBird Kindergarten all the way up through Primary Math 6B, and are now using Discovering Math. For the first level I used, I bought the textbook, and have not done so since. We use only the workbook. The only place where this was a bit tricky was when they introduced bar diagrams, and I kind of had to infer their use from the first item of the problem set in the workbook. I have referenced the textbooks once or twice at other levels, mainly because someone later gave me some stray textbooks, and since I had them, I figured I might as well check to see if we were following the model. For the secondary level books, we have used the textbook, but not the teacher's guide, workbook, or test bank book. I bought them on approval, and did not find them to be necessary.
From our experience, grade acceleration does not necessarily amp up the peer social issues. It depends a lot on the child, the receiving classroom(s), and the amount of acceleration (really, the age difference between your child and the others). It is possible to become viewed fondly as the class pet, if the age difference is larger, or if there are particularly caregiving kids in the group. While not exactly the ideal peer social situation, it isn't exactly bad, either.
Also, at some point, it may be that so little time will be spent in the home classroom that it will become de facto grade acceleration.
And, BTW, anyone who thinks it is possible to run out of things to teach is giving you a pretty accurate picture of how little they know.
