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.
Are you sure that Ethereum will go down in the near future? because according to news from several people that tomorrow there will be a London hard fork on Ethereum and everyone predicts that Ethereum will continue to rise in price.