One, the sensors. These could be anything we'd like (barometric, temperature, humidity, whatever), and there would have to be a lot of them. They'd be compact, durable, and reprogrammable to repurpose them for other things, but we'll get to that. They would be powered entirely by radio flux, possibly with a secondary radioisotope-powered transmitter in orbit, and we'd achieve that by having very long, very thin antennas attached to each.
All of these are useless for navigational purposes, but that has been said before. Additionally, your sensors are going to have a very hard time not to freeze to death, as radioflux, aside from being impossible to google without getting irrelevant results, isn't the most energetic power source.
These would unfurl as draglines - the sensor modules would be shaped like spools, grooved aerodynamically to spin as they entered the Martian atmosphere, throwing the wound antenna outwards forcefully as they descend - as they slow, the antennas would naturally start to pull more and more, putting a large amount of its momentum into rotation. There would have to be no other method slowing them, so yes, the sensor would impact with a certain amount of force.
If we made them rugged enough (with well-engineered sensors), that could actually help them find purchase in the soil once they hit. Some of them would probably fail, but we're trying to prevent the same thing from happening for colonists. It's an unknown to me, but since there's no complicated robotics, I'm reasonably certain we could work something out.
The martian atmosphere is very, very thin. It's doubtful that they'd get any meaningful spinning energy, without taking a massive (in comparison to the probe) wind catcher. Additionally, it's even less certain that it will survive. The martian escape velocity is 5 km per second. With no significant braking systems, Your impact speed would be comparable. Even if it were an order of magnitude smaller, the probe would still be destroyed.
So now we have a loose network of transmitters scattered across the surface of Mars. If you made the mission large enough (which, lacking the need for crazy heat shields and sky crane maneuvers and chutes etc etc etc, you might be able to make this system quite thorough), you would now have the beginnings of a communications and locations system. They could act as primitive relays to allow future martians an emergency comms system that would "never" fail. Because Mars has no magnetosphere, they could act as doppler weather stations for a suitably equipped orbiter (and this is also why I think that a RFID-type setup could transmit powerfully enough to work, correct me if I'm wrong) If you'd like, they could be repurposed as a great big radio telescope, which could provide for another source of data for solar activity, or just for Science. I'm sure people could think of other uses for a bunch of antennas attached to computers. It'll probably end up being Martian WIFI, which is probably a sanity saver for colonists.
Even if your probes survive, they'll likely be buried several meters deep into the ground. (Your proposals shares some similarities with a prospective project to rapidly install underground sensors ). Most will end up in small craters. Additionally connecting them toghether is going to be hard, as they'll need orbital sattelites to bound there signals too.
This is why having them be reprogrammable would be a good thing. Raspberry Pi anyone?
Raspberies, and much other customer electronics fail after consistent exposre at minus 20°C. Average temperature is -55 degrees.
Distributing this system properly would benefit from some better planning than just letting them all go at once. I would suggest a single sensor be sent down to gather weather data in the local area, and then an additional one should be dropped each time mission parameters are reached where they could be reasonably sure that the sensor would not veer off-course. If there was significant drift from wind activity during the descent, this process could be sped up, and if we notice them drifting together in certain spaces, that would be an indication of a more established wind pattern.
Martian atmosphere is not sufficiently dense to result in weather having any significant influence. The only thing you would want to watch out for is a dust storm.
What do you guys think? I just think that we can do better than another rover. Particularly now that we've found water, and philanthropists seem to be interested in dipping their toes into exploration on their own, it seems like a waste to send a nearly identical mission just because we don't feel like spending money to develop other ideas.
Honestly, the premise is flawed. A sensor network is great, but they won't survive the harsh environments. Additionally, their original purpose is useless too.