Expected a price drop on all 4xx series soon with CES announcement of RX500 series ...
Spend now or regret later for setting new rigs? Usually we can see after announcement within 4 to 6 months.
In 4 to 6 months you could still mine a considerable amount and also, there are coins that you won't have the opportunity to mine that well.
Look at Monero next year in April 86% of all coins will have been mined, from that point on you bet that it will become less and less profitable to mine it if the value doesn't skyrocket. If it does skyrocket the people that mined now would also make a ton of money. This is just an example, there are tons of coins like this.