They were always designed to be nothing more than debris from the moment the rovers cut the last umbillical with them before leaving. They're brainless, powerless, communication less strucutres with no purpose but to cocoon the rovers during landing.

To add cameras, wind sensors etc would require power ( so solar arrays, which would have had to be driven over by the rovers and thus probably broken ), a processing unit ( the rover had all the brains ), batteries (to survive over night ), communications equipment, insulation, perhaps 30, 40kg of added mass ( when there was no mass budget to be had ) and volume ( when they were already the most volume dense vehicles launched to Mars ) - and that's before one adds any instrumentation. Cameras? What's the point - we've seen the terrain from that perspective from the Rovers. Balloon? - they'd have to be very large to work on Mars. A deployable balloon would instantly take up the entire volume within the tetrahedral structure.

Once you've added cameras, wind, temp and rad sensors and a balloon inside that volume, you can throw the rover out - it's never going to fit - you're basically asking for the Mars Pathfinder lander design, inclusive of its payload on the base petal - AND a rover...it's never going to work.

In terms of mass, volume, power, money, time....it's a non starter.

However - a network of dedicated static long-life landers for meteorology, seismology and other sensing is still a 'must do' on the Mars exploration program. Using the discarded landers isn't the way to do it though. It's no more of a waste of hardware than the heatshield, backshell or parachute however. It's hardware that was designed to do a job it needed to do and no more, and it did it perfectly. No more, no less.

Doug