It is very possible that spin-offs don't have a big future.
I just think you're advertising spinoff coins with distribution based on the existing BTC block chain in completely the wrong way. They shouldn't be referred to as altcoins, their main usage will be an insurance plan for Bitcoin itself. If and when things like transaction fee only block rewards fail to incentivize miners to keep the block chain secure, you can have a fully functioning backup system with 1% annual increase (or other magic number) ready to go. The problem is, Satoshi doesn't like magic numbers.
I think you've made a very good point here. Spin-offs can be used as an insurance mechanism (or as a blockchain-preservation mechanism) to protect against a black swan that could affect the bitcoin network, or to permit some "tweak" that would be otherwise impossible. I agree that I've been promoting them more as a non-threatening platform for innovation, but I should add balance by advertising their potential as an insurance mechanism too.