Sidechains have issues in the current incarnation that we have been shown; they need to be mined and a 51% attack on Bitcoin will enable the miner to gain access to the coins that are in the Bitcoin blockchain waiting for release via the two way peg.
If these issues cannot be solved then Vitalik may be correct that Ethereum based side chains might actually be a better way as it seems Ethereum is designed to handle this type of advanced contract.
Either way, whatever coin (bitcoin or ether) implements these side chains safely and correctly will likely win as being the foundation for the future of cryptocurrency/platforms.
The side chain idea allows the native cryptocurrency to compete and win out over other competitors. Want faster confirms? Use side chains. Want Zerocash anonymous transactions, peg into Zerocash and peg back out again. I believe the future will be a battle between Bitcoin and Ethereum with a major war zone being sidechains.
Also consider this: If cryptocurrency can have on top of itself many other applications built (decentralised: {web hosting,web app hosting, databases, information, computing engines: {search, math, compute}, contracts, code}) then does that coin itself eventually gain 'intrinsic' value via being the foundation of all these new systems?
Imagine a TOR that is based entirely on the greed incentive and not just good will, where the entire system is an Ethereum contract. Imagine an open source google search where the code is run entirely on top of the nodes and each search costs 1 cent in ether to be paid to the nodes for hosting and running the code.
If this happens, that coin becomes pegged to a brand new internet running on top of blockchains. Just something to think about.