My default on all propositions is always No for this exact reason. It's a change to the constitution of the State. I feel like that should have a higher threshold than "eh, sounds good".

Absolutely. And I do still vote for some propositions if I think they’re a great idea, but with a much higher bar than for other decisions:

If a proposition is a good idea and the people turn it down, they can try again next year.

If a proposition is a bad idea and the people vote it in, we’re stuck with it.

The cost for saying “no” and being wrong is much smaller.

Can a new proposition override (or cancel out) an older one? Are they similar to Constitutional amendments (such as 21's canceling out 18'th) or are California props more sticky?

Yeah they can override old ones. That's pretty much the only way to change the old ones -- pass a new one that overrides it. The legislature can't override constitutional amendments.

In case anyone is curious, there are multiple different kinds of California ballot propositions. Some are constitutional amendments; some are statutes; some (like the subject[s] of this particular comment thread) are a combination of both. There are also bond measures and veto referendums, which for the purposes of this classification are probably more like statutes than amendments. (Furthermore, the ballot propositions can be citizen-initiated, legislatively-referred, or mandatory.)

On the ballot for 2022 in California is 1 constitutional amendment, 2 combined amendments/statutes, 3 statutes, and 1 veto referendum.