There really aren't a lot of ways that one cantilever brake can be substantially better than another. In theory some flex more than others, and that might rob a little of your braking power. Some have nice features like barrel adjusters built into the straddle cable attachment mechanism. Some are a bit lighter than others. Some look better than others. The biggest difference, though, is in design (i.e. brake geometry). Skip the next paragraph or two if you don't want to think about brake geometry.
Cantilevers allow for nearly infinite adjustment in mechanical advantage, so whatever you have you can tweak them to have more power or more wheel clearance. The biggest variable is the width of the brake arms. Wider brakes like you have have a wider range of setup parameters in which they don't completely suck, but within most of that range they are less responsive to adjustments. Low profile brakes have a narrower acceptable range, but a higher maximum mechanical advantage. Medium profile brakes (like the CX70) attempt to strike a balance between these two. Look at the graph on the MAITOY link and you can kind of visualize this.
Anyway, what I'm getting at is that braking power is a function of mechanical advantage, and mechanical advantage is determined by brake geometry and straddle cable height. That said, too much mechanical advantage will make the brakes feel terrible.
I haven't actually crunched the numbers, but a brake like the CX70 probably offers a bit more mechanical advantage than you can get without having the straddle cable really close to the tire on your wide profile brakes. The trade off is that if you don't have it set up just right it will suck. Shimano attempts to mitigate this trade-off by providing you with a (nearly) idiot-proof setup process. They give you a fixed length link wire (like a straddle cable but slightly different) and have you measure a few things on your bike to select the right spacer combination. If you follow the instructions, you get pretty good performance out of the brakes.
I think the CX70's offer more stopping power than the Tektros you have (which I believe are CR720's), but they don't allow as much clearance between the brake pad and the wheel as the Tektros. I've done a lot of muddy CX races with the CX70's and have never been bothered by that. Shimano did a nice job of getting most of the brake body away from the wheel and that's where most mud accumulates anyway. If you aren't racing or riding otherwise through muddy fields, you probably don't care about that. Another thing you might not notice if you don't race is that it can be easy to catch your leg on the rear brake as you hop on the bike with wide profiles in the rear.
I also think the CX70's are really nice looking, though I understand opinions about that vary.
In short, I think the CX70's are a nice upgrade over the CR720's, but you can almost certainly get acceptable performance out of the CR720's. If you tuned the brakes you have for optimum stopping power, you probably wouldn't notice a huge improvement with the CX70's.