A coin would be expensive when Bitcoin price is high. Normally all the altcoins would follow the path of Bitcoin whether it is low or high. Some coins reflect the price drop or high instantly and some may have impact bit late like two to three days or a weeks time to reflect in it.
To answer your question asked in the topic, December mid week is the season where all the coins would be in peak price.
I also believe that mid-December is the best time for high return coins. so I think coins will be expensive and the benchmark coin can be expensive is to follow the bitcoin groove.