The factor to look at is how many BTC you can get for your money. AFAIK, buying has usually been more cost-effective.
Agreed, but as we can see, the difficulty won't rise all of a sudden, and so, for some time, we may get a fixed amount while mining those coins and an ROI, save them and wait for the prices to jump high as no one in the previous year knew that it would go that much, but it did...
You are also right that buying them low and selling high doesn't involve much risks such as electricity bills, difficulty, price, mining hardware, etc...
Appreciated... +1