I understand it takes longer to find blocks.
Is there a point however where there is no hope of finding a block in any reasonable timeframe?
For instance if you are on a pool with only 3-5 miners. And hash rate (phi algo) is in the 300 MH/s or less range. Is it a complete waste of time?
There is what you called a pool luck, a probability for mining, there are computations on how to determine a supposedly mining blocks for a pool.
see this thread
https://bitcointalk.org/index.php?topic=1754314.0take a glance with #3 stated by xhomerx10 kudos to him
3) nothing as it is random and unpredictable - though if it is continually unlucky perhaps you should avoid the pool