It's all true, but times are changing. Soon it will be cheaper, as lift cost drops, to just send a thousand cheap, heavier probes towards mars... than one super engineered probe.

But with a thousand probes you still might not care about dusting the panels off. It all depends on how long you need the probes to last. Mass savings will still be important, in the same way material costs become more important when mass-producing something than when making a one-off.