Are population bottlenecks ever beneficial?

They possibly could be if the individuals left over are extremely fit and their fit genes do not lead to genetic diseases. Practically, I do not think this ever happens however.

The problem with population bottlenecks is the reduction in genetic diversity. When individuals are lost, the alleles they carry are lost forever. If this process occurs enough, the population can suffer. When genetic diversity is reduced, individual alleles that may ordinarily be immediately removed can be increased in frequency. On the other hand, some other positively influential genes can be increased in frequency and can increase the fitness of the population overall. The problem with making a "rebound" in the future is that the genetic diversity is stuck at what it is until evolutionary processes like drift, mutation etc can create new genes or significantly change existing ones. Increased occurrences of gene mutation are not always bad or good for that matter. Many mutations are silent as they do not alter the order of amino acid placement (ie they change the codon to another one that codes for the same amino acid).