Can we trade a little security for wider adoption? Would wider adoption make it more valuable? Nobody knows.
How much will the value of bitcoin drop when people realize it can never scale? Nobody knows.
You aren't sacrificing wider adoption of Bitcoin. You are sacrificing wider on chain adoption of Bitcoin.
Bitcoin can scale perfectly well with off chain transactions. History has shown us this when the "off-chain US dollar" was backed by "on-chain gold."
Your trading a little bit of Bitcoin security for adoption is akin to making the gold more easy to counterfeit.
IMO off chain for serious stuff is trouble and defeats the purpose of Bitcoin, we may as well stay in fiat if this becomes a norm.
The side-chain (off-chain) solutions are also a compromise between performance and de/centralization, and logically it becomes a rats-nest:
Consider the case where 1MB is the block size limit and global bitcoin tx volumes are high enough to require 10MB blocks. Then at least 9 sidechains are needed. Unless one sidechain can have 9MB, or even 10MB blocks, which begs the question of why the BTC mainchain can't have 10MB blocks! Also wouldn't a 10MB sidechain just take over from the crippled 1MB mainchain?
If the offchains or sidechains are centralized in order to raise performance then there is a central point of failure (and central point for surveillance, and central point for government kill-switch) for 90% of the bitcoin transaction volume. This defeats the whole point of the decentralized peer-to-peer network. If the off-chains/sidechains are decentralized then they need a large network of full nodes. Where are they coming from?
Gavin's testing of 20MB blocks shows that loading (disk io) for these is 4x faster than 20 1MB blocks. So there are economies of scale which are not easily seen with lots of sidechains. The off-chains/sidechains may have a role for micro-tx or faster block times, or 2.0 data storage, but don't help with handling tx volumes while still maintaining a fully decentralized payments system and currency.