Are there anyone who would be unhappy with doubling the shift size? It would make unpaid shifts much more rare.
The point of this debate should be about netting the pool a higher average hashing rate. Increasing the shift size will decrease the chance for unpaid shifts, but it will also decrease a renters potential maximum payout as it is tied directly to the shift size.
My vote would be to leave it as-is. Don't fix what ain't broken.
I do concur with scyth3. However, based on my previous assessment, I would also opine that having a greater risk versus reward ratio will attract more renters looking for a higher potential payout and will therefore increase the pool's average hashing rate.