As someone who has worked as a programmer in the CC industry, your generic "auto allow all disputes < $30" isn't as generic as you think.
Yes, for a member in long term good standing, it's cheaper for the CC to just eat the charge than to research it. The merchant isn't affected and gets paid.

But part of a customer remaining in "good standing" includes an extremely small percentage of disputes.
To turn the tables, the analysis isn't the amount of the charge vs the cost of researching its validity ($30 in your example) ...
It's the amount of the charge vs the revenue your history has proven you can bring to the CC.

Is it worth it for the CC to ignore one (or two) insignificant charges to retain your business ??
The revenue you generate gets less each time the CC has to absorb a minor charge.