The priority is still air sealing and insulating the house. Yes, the stack is 24/365 parasitic load, but as a fraction of the current overall heating bill isn't all that high- a low to mid single digits percentage.
Later versions of the P206 with standing pilots came with stack dampers integrated into the ignition controls that "prove" the damper is open to enable the ignition. A simple retrofit stack damper is easy enough to cut in, and could be worth a couple percent of the bill, which might be considered at some point. If by some stroke of luck they manage make the place tight enough to need more makeup air for the stack to operate correctly it's cheap & easy enough to add a zone-damper type ducted proximity vent (to be proven in series with the retrofit stack damper) if it comes to that.
So it depends on what the goals are here. From a net present value of future energy savings point of view it's hard to rationalize doing anything but tweaking the existing boiler. From a comfort improvement point of view it's almost always better to spend the first tranche of home improvement on the house itself. At some point the house might be tight enough to force another decision point (is it time to add a makeup air damper or just get rid of the thing?). In homes without air conditioning that decision point might come when it's time to install the AC, making it a heat pump instead.
Yes, real radiation (rather than convectors) comes with real comfort benefits, even at sub-90F water temps.
But it is not necessarily "worth it" in everyone's book to buy better radiation (or even a retrofit outdoor reset control), especially when there is still plenty of other low-hanging fruit on the building efficiency front.
It IS worth it to most people (once they understand it) to improve the air tightness & insulation of the house, which shrinks the room to room temperature differences, and makes it easier to control heat and moisture transfer through the house, and to control indoor air quality, etc. On a house this size getting the blower door tested air leakage to even <<2500 cfm @ 50 pascals (lower is better) can do wonders, and most homes built in 1967 aren't there yet.
