I disagree. Some miner machines like myself do run full node eth mist wallets and other staking coin wallets that requires a lot of hardrive space. 500 gb ssd is cheap and affordable now.
I also like to surf the web and do trading so having a decent enough cpu is nice while I'm still mining.
Why would you serf and trade from a dedicated mining rig?

Especially from one that costs $30k? Running wallets on mining rigs is also not a good idea in general since you can't always trust new miner software and never know for sure that it's not infected with the code to steal your wallets.
Running a regular PC that also does mining sure, in such a scenario I totally agree with you, put as good CPU/RAM/SSD in it as you want. But doing all those things you listed from a dedicated mining rig? I guess, if you have $30k for a rig like this, you can surely afford a proper desktop/laptop for general computing.