I think they make much more sense for lower income folks.  If your income is below the standard deduction, do a partial Roth conversion and still pay $0 tax (although at that point I'd probably use the 10% bracket too).  If the balance in the client's IRA is large enough that RMDs are going to make SS taxable, you can do Roth conversions in their 50s & 60s to get the income out of a taxable IRA and keep the SS income taxed at 0%.

But you're absolutely right, mathematically you're just playing "guess the tax rate."

I've read articles about the psychological aspects (not sure how much I buy into them).  In your example the taxes were paid out of the Roth at conversion ($1,000 becomes $800), but this also becomes an opportunity to "invest" the other $200 from outside funds so it becomes a forced savings (I guess psychologically most folks instead of saving the money would just spend it on hookers and blow?)  And on top of that, the forced savings grows with 0% tax in the Roth.  At least until Congress decides they want to start taxing Roth earnings. 🙂