I just came across some apparently new pages in the #1 Club Gold members-only section of Hertz.com (see https://www.hertz.com/serv/gold/member/goldsumcomp.cfm ).
They've apparently added two new levels above #1 Club Gold - - Five Star, for renting at least 10 times in one calendar year, at President's Circle for renting at least 40 times per year. Each level offers one-class upgrades (guaranteed for President's Circle), free rental certs, savings coupons, etc.