A "cash-out" refinance is just borrowing more than you currently owe, and "buying points" is just prepaying interest upfront. How good a deal the points are depends on how long you plan to keep the mortgage. Typically the points have about a 5 to 10 year payback period, so you would need to keep the mortgage at least that long to make the points worth the upfront expense.
The actual math behind points is not that simple, though. They're priced based on the "present value" of the interest savings based on some discount factor which should be pretty close to the APR of the loan, otherwise it would be a bad deal either for you (and you wouldn't take it) or the bank (and they wouldn't offer it).
So I can't see where borrowing more just to prepay interest would be a significant savings overall. You're essentially borrowing more to pay interest upfront. So it's only a good deal if the effective interest rate of the points savings (which you'd have to calculate yourself) is significantly lower than the APR of the loan without points. In other words, the interest you pay on the extra borrowed amount would have to be less than the interest saved from the lower rate.
Also, cash-out mortgages tend to have a higher rate than pure refinances since a cash-out indicates a more urgent need for cash, so it's even more unlikely that you could come out ahead by buying points with a cash-out refinance.