Agree, he is very biased and hard to deal with, but his posts are well worth reading.

Well, that's correct if 'breaking' means finding a way to almost instantly calculate hash value. But imagine that a way to instantly find a collision is found. Bitcoin code (on which almost all altcoin wallets are based) prevents duplicate block hashes, but one can 'borrow' valid block hash from another blockchain with the same PoW algorithm and reuse it. Another question is where and how inject arbitrary bits into block header, there is only 32 bit of nonce and something like 14 low bits of time value, so this attack is rather theoretical for now. Quick conclusions - the first hash in chain should be the strongest one, high difficulty blockchain could damage its weaker siblings with the same algorithm.

Point is, if there's less heat, then something surprising is going to happen. Basic common sense. Watch the Groestlcoin

I think no, as long as PoW hash is not used to calculate Merkle root, but even this would be almost insignificant. And most altcoins use old good double SHA-256 for transaction hashes, IIRC.
Orphan rate is an excellent topic, I'd be glad to see a good discussion about it, though I have almost nothing to contribute to it.

Very interesting! Could you give a link to discussion?