Damn, thanks for that lengthy and comprehensive response--big confidence builder as it (more-or-less) confirms a lot of my assumptions regarding the concerns in the system. A decentralised backbone upon which other systems can be built seems like the right choice if decentralisation is something which we value. Second-layer solutions that make tradeoffs of decentralisation/whatnot to meet the demands of higher capacity can happen (and already do--just look at all the off-chain trades on exchanges) on top of a decentralised ledger, but second-layer solutions cannot return decentralisation to Bitcoin if it is lost.

Honestly, I'm going long on Bitcoin anyhow (most of my transactions involve combining small outputs from altcoin mining), so current usability/capacity concerns aren't especially pressing for me, especially with huge improvements in these areas already in development. It will be an experience to see how this plays out over the next few years--just what will Bitcoin look like by the 2020 halving?