I once drove too fast near a cop and they didn’t pull me over, therefore speeding is legal. And the law doesn’t define specifically what acts can “cause a disturbance”, so that means you just can’t be arrested for it. Right?

Cops regularly miss violations or just don’t feel it’s worth enforcing them when they may have more important things to do. And laws that don’t define specifics mean the laws can generally be applied broadly, not that they can’t be applied at all. You’re in more danger of running afoul of a law that doesn’t define specific acts it applies to, not less. You may be able to get the case thrown out in court if they consider it too ill-defined, but that’s the sort of thing you pay an expensive lawyer to argue, not a reliable get out of jail free card.

All that said, you’re actually right about apparel not being considered electioneering in Pennsylvania. The reasoning for why you came to that belief is bad, but the end belief is correct. The actual rules from the Secretary of State, both say apparel is electioneering:

Watchers may not engage in electioneering while inside the polling place, which includes wearing apparel or accessories that signify support for a candidate or party.

But that it should not be used to prevent people from voting:

Enforcement of the prohibition on electioneering should not prevent eligible voters from voting. Thus, in the Department’s view, individual voters who appear at the polling place to exercise their right to vote are permitted to wear clothing, buttons or hats that demonstrate their support for particular candidates.

So as long as you’re in the act of voting you’re allowed to wear blatantly political clothing, but if you’re just hanging out by the entrance you’re not.