There's desperate, and there is 0.4BPs desperate.
Remember folks, you are essentially paying 0.4BPs for any other option - in case of MM, that means that two things you get is a chance to make a long shoot on priceless treasure and no enemies from scamming(you might not even get any, depending). That's all you get for that expenditure.
Is that really worth 0.4BPs? That's halfway through to some of amazing bonuses that would either skyrocket our Cultivation speed or make us much, much stronger in the long run. That's +0.4 to our stage stats, if you take Might as benchmark. Would you vote not to take +0.4 to your stats in order to get chance at treasure and no enemies?
Well, we know that Priceless Treasures can be worth multiple BP, but as I said, that's not my main motivation here.
We're not actually guaranteed to find the lich, and we need to come up with a plan to make sure we do. I think that spending a Mastermind Point can make it much more likely that the fight plan will allow us to find him and place Nameless in a strong position when we do so.
The chance of Treasures does give us some diversification of the risk of walking away from this empty handed as well. This is a lesson that Nameless should well recall from his previous lesson. Diversifying your investment portfolio can reduce your risk without reducing your reward.
One Mastermind Point is generally worth around 0.5 Beyond Points. Losing a Mastermind Point in return for 0.4 Beyond Points seems likely to be a ba deal.
And, as I say, the value of a Mastermind here is the guarantee not to be caught/make an enemy when scamming, which means we can make very aggressive use of scamming and its results for the Direct plan, with much less risk of failure or back fire.
Counter argument of, IF we get the priceless Treasure, we know they can be worth an ENTIRE BP. So one could argue going for it for the chance of something worth a BP.
Well, technically, a peak Priceless Treasure is equivalent to an EFB, so ten Beyond Points.
It's vanishingly unlikely we'd get one that good of course, but even the chance for one at all is a good reward. As a baseline, the chance to get a Priceless Treasure was a feature of fief management, not murder hoboing.