Protector practice - not just DS practice, but any proper protector practice - does not necessarily "improve" one's outer conditions. One could just as well lose one's wealth (or societal position, or one's spouse, etc.) The idea that Protectors give stuff and goodies is wrong. They can simply take it all away as well. Protectors' job is to give the proper conditions for practice, and if that entails giving you a Ferrari, you will get one, but if that entails losing your previously owned Ferrari, you will lose it. Protector practice is a gamble, samsarawise.
As for karma, we all have karmic seeds for both enjoyment and suffering, so protector practice merely ripens the seeds that we need most, at that time.
I am speaking now about proper protector practice. Merely giving gifts and praying to some Dude-in-the-sky is not necessarily proper practice.
(And as for karma-theory in general, not everything that happns to us is caused by our karma. While it is true that all that we do (karma) has a definite effect (karmaphala), not everything that affects us is caused by our karma. There are freak accidents, and the universe is non-deterministic, so some stuff just comes, whether we have done something or not.)