Checked out your recent fish room video, sounds/looks like you have a number of tanks, including a 120. All in the same room? Do (or can) you keep the door closed to the room? I"m thinking it may not take anything too drastic to fix this...
If you've ever been at a lfs or breeder or other fish room with no air conditioning, you know how they're typically warm and humid or how some of them have to have a fan blowing through the room to keep it from getting too hot. Also, in my house when I have a small/medium sized room with a big tank or several tanks, closing the door can keep the room several degrees warmer than the rest of the house in the winter. In other words, if you have enough gals going in a room, just closing off air conditioning vents and keeping the door closed (if it's possible and you're not doing this already) should make a difference in ambient temperature. Also, if there's a way to let sun in the room or directly into a tank, it gives you some passive solar heat-- and there's actually some benefit to allowing solar UV into a tank, degree of benefit depends on exposure.
Also, no necessity to replace all your heaters. It can be done just for the tanks and fish that need it most, and not even all of those would need a new heater-- for this reason: Whenever you upgrade a heater in one tank you now have an extra or supplementary heater for another tank if it needs it. In other words, assuming you're replacing a working heater simply because it's not enough for a particular tank, each new heater you buy gives you second heater (the used one) that can supplement another tank. So, assuming the old heater is still in good working order, but just not enough for the tank, one heater gives you two, two gives you four, etc.
The other thing I'd do is figure out which tank/fish really needs warmer temps and which don't. Wimpiest heaters can go in tanks that don't need to be warmed that much and better heaters in tanks that need to be warmer. Depending on your fish, some can be just fine at cooler temps than most people think.
Good example is angelfish. Lot of people think: they come from the Amazon, so they need temps at 80 or in the 80s. But healthy (scalare) adults will do just fine at 72-74 ime, although they like it warmer to spawn. Or take discus. Everyone thinks they have to have constant temps in the 80s, but in the wild many experience temps in the 70s, some under 75. (
Link) (not saying you should keep discus at 74 degrees, just that wild discus tolerate much lower temps than most people realize).
Part of the trade-off with temperature is at warmer temps within their range fish tend to grow faster and spawn more, at lower temps they tend to grow a little slower and live longer. Also, lower temp and slower metabolism means less food needed, cleaner tank. Immune system is better at warmer temps for some fish, others are stressed by warmer temps. So there's not always a single right way for every tank, but you don't always have to go with common 'wisdom' for what temps some fish need.