Investing into bitcoin is not the same as trading bitcoin, you have to first decide which one you want to do before you put any money into crypto. If you want to trade, as in get in at the current price and increase it 10-20% and get out, that means it is trading and if you want to do that you may wait out a bit, or you may even get in right now because it looks like it could go up a lot as well.
I believe 10-20% is a big change for trader because from what I have seen traders feel pretty good with even a 2-3% change in price because the price of bitcoins is high and even a 2% change means hundreds of dollars change which is enough for a trader to earn their profits. I agree that it might be a smart move to wait out a bit but surely around the new year we will see a price hike in my opinion so even buying now is not the worst idea.
However if you want to invest into bitcoin, like put your money in it right now and wait few years at least before you even think about selling, it would be easier for you to actually invest right now because you are at the very start of bitcoins big increase towards institutional investment to become a wall street thing, if you get in right now before that happens you are going to be very lucky.
You mean long term investments and for investing in long term I agree with you that anytime we can buy because we are not going to regret that we could have grabbed the same amount of bitcoins for a few hundred dollars cheaper.
For a trader it is a big lose if they miss out on even a few hundred variance so depends on the need and the purpose of purchase.