If STEEM's price keep decreasing or steady, one will need more SP to generate similar amount of VP for selfvote and curation. Since more STEEM are powering up everyday and STEEM's inflation rate is decreasing, rewardpool is a getting smaller. One needs more SP to sustain similar earning which is not sustainable.

However, buffer for 6 months income can help since it is long enough for STEEM to up or down 3X. Sell some at high, consume some, and buy some STEEM back when it is down. Its easier to say but hard to implement.

Other income such as Masternodes, crypto-trading, mining can diversify the risk too.