Most cichlids should be in water around 78-80 degrees, 61 to 70 is way too cold to keep them at for an extended period of time. I have no idea what you mean by "looking happy and active" - can we please see some pics? How big are you fish? How many years have you owned them in these conditions? How are their colors? Just because they are alive and swimming around does not mean they are comfortable or healthy, and many cichlids are long-lived fish, just because you've kept them for a couple of years in this situation does not mean they will live out their full potential.
I mean seriously, go spend less than $50 on a few heaters, and your fish will be much healthier, and again I'd like to see pics - I guarantee they will look a lot better too. It kind of gets to me when people own, apparently as you do, a whole lot of fish, but just can't be bothered to spend a couple bucks on a heater.
I guess since you say if you had expensive fish you would use a heater, that you have no problem losing your inexpensive fish because the water is too cold? Because heck, you can just go out and keep buying another and another? How many fish have died in your tanks in the past few months? Again, how many fish have you kept for several years living well and healthy in those conditions, and can we see pics of your tanks?