The removal of the ability to reserve spellcasting test dice for drain is probably the best thing they did to the magic system in 4th edition. It was so easy to imbalance spellcasters in SR pre-4th. I would hesitate before doing much to change the size of drain pools.
The closest we come in my home campaign is a house rule that allows spellcasting, summoning, banishing, and binding foci to apply their bonus dice to either the initial test or drain test (incompatible with a power focus in either case). That was done to add value to non-power foci, because the marginal increase in costs of power foci combined with the exclusivity of using one focus per test was making people ignore pretty much any focus other than counterspelling, power, sustaining, and weapon foci.