I think a mid-long term investment is a good way to look at Steem. Probably more mid-term than long. "Retirement plan" depends on how old you are. If you're 18, then you may suddenly come into some good money if Steem moons in 5 years for example. Then in that case I'd advice you to leverage that cash to do some basic things in your 20's like - Pay off debt, travel, start looking at real estate... etc.

If you're closer to 60, and you're debt-free, then you may be looking at leaving something for kids (if you have any), or finally buying that yacht to sail to that Island near Zanzibar :)