Answering my own question here, but after a bit of noodling around, I found a cheap (less than $100) security recording system to replace my ancient one, drop in a hard drive, so decided to give it a try. About a fifth the weight, a quarter the size, lots more capabilities, takes both analog inputs and some digital/IP cameras (limited number though). If I were starting from scratch would probably go all digital but being able to use what I already have wired made this an easy decision.

Terrible instructions with this unit, but eventually figured it out, and now I can see what's on the cameras from away on my phone. The only extra expense was that it made more sense to replace the ancient monitor (old connections, no hdmi, terrible image and burn-in), so a small cheap digital TV sacrificed, as it also fit the wallmount space and vesa mount perfectly.

I had meant to measure the power draw on the old ones and forgot; given how big and old and hot, I could argue that on electricity alone they'll save some money (okay, likely not much). At any rate was only a matter of time with the old system - even the old hard drives it uses are increasingly hard to find and expensive (for what you get). I was pretty surprised at how much smaller and lighter newer gear is in comparison - not to mention reasonably priced.