Since Aug. 7, the CurrencyShares Japanese Yen Trust (NYSEArca: FXY) has tumbled 4.5% as the yen has hit a series of six-year lows against the U.S. dollar.

So precipitous has FXY’s slide been that it was just one of 21 ETFs to hit a new 52-week low on Wednesday. Predictably, a sliding yen has been a boon for currency-hedged ETFs such as theWisdomTree Japan Hedged Equity Fund (NYSEArca: DXJ) and the Deutsche X-trackers MSCI Japan Hedged Equity ETF (NYSEArca: DBJP). [Stealth Rally for Yen-Hedged ETFs]

However, as those ETFs have impressed since Aug. 7, many investors are missing out. DXJ and DBJP are up 6.3% and 6%, respectively, over that period, but inflows to those ETFs suggest some investors need some more convincing regarding the yen’s current spiral to multi-year lows. Since Aug. 7, DXJ and DBJP have hauled in just $49.3 million combined.

Ongoing yen weakness could spark new inflows to Japan hedged ETFs. DXJ has suffered significant outflows this year, something those short shares of WisdomTree (NasdaqGS: WETF) have not been shy about pointing, but new inflows to the ETF spurred by yen weakness combined with inflows to the WisdomTree Europe Hedged Equity Fund (NYSEArca: HEDJ), something WisdomTree bears have been loathe to acknowledge, could lift the stock. [Global Markets Could Lift WisdomTree]

Investors are missing out on other opportunities. While they have been right to yank $16.7 million from FXY since Aug. 7, none have had the fortitude to embrace the ProShares UltraShort Yen (NYSEArca: YCS), which tries to reflect the daily -2x or -200% daily return of the USD/JPY currency pair. YCS is up 9.3% since Aug. 7, but investors have put no cash to work in the fund.