If you are choosing it for long-term investment then you can buy it at any price, but if you want to invest for the short term means you have a short profit target then you should wait for a dip because It is now very high.
Totally agree with you, it is never a bad time to invest in coins like bitcoin and ethereum if you are planning to invest for a long time holding purpose.
But yes for short term, ethereum has just rose so It would be much better to wait a bit for it to dip again and then buy some of those.