Yes, if either of the following criteria are met:
a) You want to hold STEEM long term for profit, the revenue generated by SP will keep your STEEM increasing.
b) You plan on being active in the network, holding SP will help you to have more weight in voting and therefore in the rewards for doing so, saving you time in building it up.

I bought in early, I got some from my old content on here and make sure to upvote here and there and my holdings have steadily increased, so I can't complain!