In my games, Time is the biggest constraint on Making Magic Items.
This is especially true at high levels when making an Item could take Months to Years to create.
You can always get more XP, Setting aside 8 months to just sit around & make a Uber-Sword is a bit more difficult.
Here is how I do it:
1. You can use the System as is. This really limits when a Spellcaster can make an Item that takes more than a few weeks to create. And a Crafter tends to spend ALL his downtime doing nothing but churning out items.
2. Power Components: You can research & find compoents that, in essence, are XP Batteries for a certain item. (ie, the Ashes f a Fire Elemetal count as 500 XP for making a Fire Related Item). You can also find Components that reduce the time needed to create an item. From the above example, Ashes of a Fire Elemental reduce Creation time by a third.
Overall, I try to be nice to people that take IC Feats. After all, I, as DM control the Time, GP, and XP players get.