Is Q-Solution required for PCR with QIAGEN's PCR kits?

Not necessarily. In a lot of cases, the uniquely formulated PCR Buffer provided in the HotStarTag Plus DNA Polymerase, HotStar HiFidelity Polymerase,  Taq DNA Polymerase, HotStarTaq DNA Polymerase, and QIAGEN Multiplex PCR Kits provides optimal amplification of specific PCR products. The usefulness of Q-Solution needs to be determined empirically for each primer/template setup, by running parallel PCR reactions with and without Q-Solution under the same cycling conditions.

Q-Solution changes the melting behavior of DNA and will often improve a suboptimal PCR caused by templates that have a high degree of secondary structure or high GC-contents.  For more details on the effects of Q-Solution on PCR amplification, please see the Q-Solution sections of the HotStarTag Plus DNA Polymerase, HotStar HiFidelity Polymerase, Taq DNA Polymerase, HotStarTaq DNA Polymerase,  and the QIAGEN Multiplex PCR Handbooks.