We have aluminum wiring in our house but can't afford to rewire it. Can we just replace all outlets/switches with co/alr ones? Is that a permanent solution?

There is nothing wrong with aluminum wiring, so long as all rules are closely followed. The three big ones are: 

1. making sure all devices are rated for use with aluminum wire;

2. no copper wire is directly connected to the aluminum; and

3. circuit breakers are sized properly for aluminum wire (i.e. #12 AWG aluminum can be protected with a maximum breaker size of 15 amps, not 20 amps like with copper wire)

Since aluminum has a lower melting point than copper, it is more prone to starting fires when wires are sized with the wrong circuit breakers. If breakers are sized properly, approved devices are used (i.e. rated for AL or ALR connections), and direct junctions between copper and aluminum wire are avoided, then you should be fine.

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