Well, risk will vary depending on the individual.   Many people were crying when the btc market cap went down by something like 200 billion USD in a during that last week or so in December 2017.

It's a good idea to hold both.   The major hassle (for me) with fiat, especially USD is that you need to trade it in constantly when they retire the older versions or bills.   This is for when you are storing cash outside of the US (in the US, it's not a big deal because you can use still use 80's and 90's bills with no problems for the most part).   But outside of the US, it gets to the point where even banks will not exchange them for you into other currencies.   I know, it sounds like 'a problem I'd like to have' but it indeed can be a time consuming labor when the amounts involved get higher. 

Not too late.   Just too late to quickly make a few million dollars in 2-3 years from $30-40k.   

Xapo, Spectrocoin, Bitstamp, Coinbase, Bitpay... there are many.   Please note that some will not be available in some countries.

Wishful thinking.   It would double the number of billionaires in the world (there are only around 2,000 or so, now).    Where will the money shift from?   From those billionaires?   Unlikely.
   

Extremely worth it from 2012 until now, especially in the last year.

As for the future, be aware that most of the people saying it is worth it now are late adopters.   It seems like it has limitless potential but there are also plenty of other alternatives now as well.    Bitcoin might not be Google, it might just be Alta Vista.

Age is not a factor.   If you don't have any capital, YES that's a factor.

Of course.   I've had stock that was worth hundreds that went bankrupt... I've had btc worth just $4 to $8... it's a market.   Anything is possible. 

The big one for me is that btc exchanges are a weakness.   You hear about them getting hacked more than real world banks.  Not sure why they can't be more bullet proof.   The other weakness is of course just like what we saw in Australia this past week...  banks can suddenly sever the link between your bank account and your btc exchange account.    These issues leave you in the limbo of not wanting to keep too much funds in your exchange account...... BUT if you don't, then you cannot truly be an active trader (if you have to move your funds to your exchange account every time you want to do trades).   I made quite a bit this year riding the waves, but would have made more if I felt more confident of letting more of my capital spend the night or even medium term in my btc exchange accounts (as opposed to air gapped and off the network entirely).   

In the spirit of this forum, I'll just ignore the thread and say... buy ETH and BTC.   Or to be more exact, I'll say it with just slightly off grammar:

Buy an ETH or the BTC and it will gain the capital in the first for.

I know even less about ethereum, but I know that the bitcoin profits I have taken this year, when put into ETH are already and will pay off quite well in the coming year(s).

I know for myself, I got into btc quite early, but I have very low tech ability, I use maybe 10% of the capability of my smartphone.   

Global reach.   Yes you can do business with just about anyone through wire transfers, but it's much more fluid when you can do so by giving people "just a bitcoin address and the amount they must send you."     No need for account numbers, names, intermediary banks, SWIFT codes, etc.   It's just 1-2 less steps but when you do a few dozen transactions a day, that is a significant savings.   Even more so for people who do even higher volumes of transactions. 

Wonderful.    Lost some profit on paper at the end, but did fairly well overall.

Yeah, I've mentioned this a few times.   That will be a serious 'check' type move (maybe not mate, but definitely a strong move).   Cut the fiat to bitcoin exchange connection and you put crypto in a headlock.   Crypto doesn't die but it becomes a lot harder to convert fiat to crypto for average/mainstream folks.   How will you send it to exchanges?   By snail mail?  By hand?   My guess is that you'll start to see more black market exchanges, which is a bad direction but sometimes if they fight dirty, the other side is forced to be dirty as well.

Nothing is impossible.   It may go that low.   Whatever the market demands is where it'll go.   That's why it's always important to take profits.  Too many people think that all you have to do is buy $20-30k in coins and then you'll have a couple of million in a few years.   Just because that exact thing was possible in the last few years, it doesn't mean that copying the exact formula will yield the same results.   

I would like travel sites like Expedia and Booking dot com to accept bitcoin.   

No problem.   Most of mine are from the $800 to $1200 range.    There will be a long line of people losing control of their bodily functions before I start to worry.

Well, at the least, all of us 'guessing' at 20K before January 1st were all wrong.   But that's not surprising as a lot of these predictions are just wild guesses.  

I would say yes, if it's disposable income, but no, if it's money that you need.