At the moment, bitcoin is too volatile to even consider adding additional risk by investing in a grc denominated asset (this includes mining). Always a winning strategy to simply hodl.
Bitcoin is too expensive now. For most people buying large amount of BTC is impossible - small fries like me only pray that they could earn from price spikes, this time possibly bigger than in 2013.
It doesn't really matter that several of us missed out on previous bubbles and previous opportunities to buy thousands of coins for small amounts of fiat.
What matters is that we can decide today the extent we want to diversify our investments into bitcoin or to invest large quantities into bitcoin hoping for a few more 10x growth periods.
There is plenty of reason to believe that we remain in the very early adopter phases of bitcoin, so we should be glad that we know about it and we are making some investments into it...
Personally, I started in late 2013, so my average cost per BTC is not much lower than the current price, even though I have gained a lot of experience and knowledge with bitcoin in the past 2.5 years.
Nonetheless, if anyone is just finding out about bitcoin today, they would likely do well to take a decent size stake into it and to research and probably to continue to dollar cost average into it, and there are quite a few ways to do that these days. After setting up the various accounts to purchase BTC, then the question becomes how much to invest, and I would suggest not to invest more than you can afford to lose, and to make a few lump investments over the next few months and then to dollar cost average by buying anywhere between $5 per week and $500 per week, depending on your budget and insuring that you are not taking away from your regular living money.