I would also fall into the “it depends” category.
I value AGR points at 2 cents each. For example, when I look at a one-zone roomette trip that would cost 15,000 points, I value the points for that trip at $300. If I can purchase the trip for about $300 or less, then I buy it and save the points. If the cost is more than $300, then I use points. Over the last few years, I’ve probably purchased more trips using money rather than AGR points by a small margin.
Of course, redeeming points means no accumulation of TQP’s, but I personally see little value in the elite levels of AGR, so that is not an issue for me. If the Select levels matter to someone, then that could move the buy/AGR line upward. When I do this same sort of analysis for air travel, the accumulation of EQM’s toward status is a very big deal for me and can often swing the decision away from award travel.