The value depends on what you spend them on. Assuming you have a card that earns 1.5 MR per dollar spent then at the low end you can redeem them for cash at about 1 cent per dollar spent.
At the high end the most productive use for points is for J or F travel where points are frequently worth at least 5 cents per dollar spent. For example, I recently used 400,000 MR points transferred to QFF to book mixed F and J JASA and FASA travel that would have cost about $17,000 to buy for cash.
$17,000 of fares for 400,000 points = $268,000 spend = return of 6.3 cents per dollar spent (plus we will also reap 380SC each from the trip)
You also need to factor in that in some circumstances the surcharge may be tax deductible which will reduce its effective cost to you.