Best Of

the boiler piping looks pretty good, changing it isn't going to do anything for you. make sure you have good venting at the end of the mains.

The savings that would be even slightly more than negligible would only happen during the once a day during recovery from setback and even then would be tiny compared to the cost of replacement so it would never pay for the replacement cost. just do it right when it does need to be replaced.

since you commented on someone else's year old post, can you show us your near boiler piping? If your near boiler piping is as bad as the piping from the op and it affects the speed with which the system heats then fixing it could be worth it.

"With the system as it is, I do observe cycling on pressure (2-2.5psi), but generally only when recovering from overnight setbacks of around 4 degrees or more."

If it only cycles coming out of setback downsizing will do nothing. I would spend the money on something else. JMHO

https://heatinghelp.com/systems-help-center/how-to-run-a-hot-water-zone-off-a-steam-boiler/

Here are several ideas of what you want to do

here is all the info you could ever need. I added two hot water radiant floor loops to my steam boiler with these instructions and I’m just a homeowner

https://www.heatinghelp.com/systems-help-center/how-to-run-a-hot-water-zone-off-a-steam-boiler/

oh, and additives in the water that make it foam.

oil on the water, improper near boiler piping. it may just need skimming. how long did the installer spend skimming it? show some pictures of the boiler and piping from several feet back.

Every once in a while some scheme for using the heat in the condensate comes up — and yours is a rather good one, as they go. Problem is… there is verry little heat to be had. Nothing like enough to heat even a very short loop.

As @mattmia2 says there, the best approach — and there are a number of ways to execute it — is to pipe a hot water loop directly off the boiler.

good idea, poor execution. you just take hot water out of the boiler and put it back in with some convenient tapings, the closely spaced tees thing wouldn't work. you can circulate boiler water directly in the hot water loop but you need to have the circulator below the water line and can't have auto air vents. you need a bypass to bypass a little return water in to the circulator so it is a bit cooler and doesn't cavitate. it will work better with a 3 piece circulator than a wet rotor because of the muck that tends to be in steam boiler water.

you could isolate it by using a tankless coil in the boiler. if you use a heat exchanger a shell and tube or small indirect will work better than a brazed plate hx.