5) Block reward = keep the same at 50, but with just one minor modification*
* You solve a block. If the current difficulty level is significantly easier than the last difficulty level, your block reward will depend on the results of performing a simple loyalty check. If you can point to a block you solved during the last difficulty era which you did not point to before (i.e., comes from the same address), you get the full 50 coins. Otherwise, you get half (25 coins). The balance of coins are carried over to the next block reward or destroyed.
Blocks are technically solved by the pools, rather than the individual miners using them, so this does nothing.
If a pool has 100 miners @ 1 GH/S connecting into it during a high difficulty era, then it gets 200 more miners @ 1 GH/S joining during an easy difficulty era, it can only point to the limited number of blocks solved during the high difficulty era to obtain the full 50 coins (the supply of high difficulty era coins it can point to, is only 1/3 the amount needed to get full credit). Naturally, the pool would have incentive to allocate twice as many shares for miners who were there during the difficult era, than miners who joined during the easy era. Otherwise, the committed miners would leave the pool for another pool who recognizes their contribution to the network, and the pool would be left idle during high difficulty times, and mine at half the rate during easy difficulty times, probably not a winning formula for a pool. On the other hand, pools may find it easier to simply not allow people to join the pool during an easy era, and only during a difficult era. Then, there will always be enough hard blocks to point to, to get full credit for easy blocks that come.