I hope I made it clear why I belive that they aren't good without some additional rules. Basically a trading a tecnical for a huge economical problem.
.)Sairon's rules + Doubling PoW reward on blocks after a PoS block AND requireing a far higher minimumbalance for PoS
Actually, I'm not clear on why you think disallowing adjacent POS blocks would be harmful - if a POS block fails, the coin age is not lost and it can be re-attempted after a POW block has been completed - with 1 minute target block intervals, would it even be noticable?
It seems like checking the type of block that occurred and not allowing adjacent POS blocks is significantly less radical of a change than your suggested doubling POW rewards for blocks that follow POS blocks and requiring wallets to be arbitrarily large to even allow them to POS. I'm failing to see what benefit those changes would have other than it keeps people from attempting malicious activity with small numbers of coins - the POW doubling just seems arbitrary..
On my additional rules in addition to Sairon's rules.
Well, there' a reason for choosing exactly double rewards* AND higher minimums for PoS.
Doubling PoS rewards woud make PoS-PoW more profitable than PoW-PoW so miner wouldn't benefit from a PoW-only currency. No incentives to fight PoS blocks (regardless if possible/profitable/...). As you noticed it's far more radical, but the real radicalism is in raising the minimum balance for PoS.
This would prevent most people from ever generating their own PoS blocks later on. The current minimum of ~20YAC to mint would be some money if YAC get's widly accepted, but for this to work it would have to be far far higher. I think a minimum of 1000YAC would be nessasary to prevent PoS-pooling and requireing fees on everyone that isn't in a pool.
Again this isn't something I want, it's something I belive is nessasary. Otherwise PoS could be pooled and miners would keep their PoS-blocks secret to exclusively mine on their own PoS-blocks. Chances of finding a block are euqual, but if they get lucky that would be a super-jackpot. Double rewards means magnitudes more profit for them since PoW mining is expensive. There is no cost for not submiting a valid PoS block.
All this wouldn't be very problematic, but since every mining pool would use pooled PoS-adresses (that are only used if a block is found by the pool) stuff get's messy and PoS isn't decentralized anymore. (Among other problems, f.e. fees for confirming a big PoS block)
*) Reducing all PoW-rewards that aren't directly after a PoS-block by 50% would have the same effect, but I doubt we could ever agree on such. I'd actually prefer that, but it's utopical that we could ever agree on such.
EDIT: Edit edits his edit... Don't know whats wrong with me today.