The A-League allows one franchise or marque player per club. Archie Thompson was Melbourne Victory's while Dwight Yorke was Syndey FC's. IIRC they allowed something like up to $1 million outside the salary cap. In our current financial state I'd presume our capacity to have one would be hindered given we've put our own constraints on our TPP.
As for free agency - it most likely won't help us either unless there was a 7-year rule whereby we could instantly add one or two quality players b/w say 23-25 y.o. to fill the hole in the middle-age bracket of our list.
I'm not a fan of free agency but if it was brought in I hope Miller remembers his former club's initiative and drums up a list of every 10-year player in the League. Anyone who debuted in 1997 or prior to that. Most are over the hill but there's a couple with a few years still left in them:
Adel - Clarke, Edwards, Goodwin, Hart, McLeod, Riccuito, Torney, Welsh
Bris - Akermanis, Bradshaw, Chris Johnson, Keating, Lappin, Leppitsch, Michael, Scott brothers, Voss.
Carl - Kouta, Lappin, Whitnall
Coll - Buckley, Burns, Caracella, Clement, Licuria, Morrison, Prestigiacomo, A.Rocca, Wakelin
Ess - Camporeale, Fletcher, Heffernan, Hird, Jason Johnson, Lloyd, Lucas
Freo - Bell, Heath Black, Cook, Farmer, McManus, Parker, Schoefield
Geel - King, Milburn, Riccardi
Haw - Barker, Crawford, Dixon, Everitt, Joel Smith
Roos - Archer, Shannon Grant, Brent Harvey, Hay, Jade Rawlings, Sav Rocca, Simpson, Sinclair
Melb - Bizzell, Holland lol, McDonald, Neitz, Nicholson, Pickett, Robertson, White, Yze
Port - Peter Burgoyne, Dew, Francou, Kingsley, Lade, Tredrea, Wakelin, Wanganeen, Wilson
Rich - Joel Bowden, Browny, Chaffey, Gaspar, Kane Johnson, Richo, Stafford
St K - Gehrig, Hamill, Robert Harvey, Hudghton, Peckett, Powell, Thompson, Brett Voss
Syd - Barry, Hall, Mathews, O'Loughlin, Williams
WCE - Banfield, Braun, Chick, Cousins, Gardiner, Wirrpanda, Wooden
Dogs - Darcy, Eagleton, Chris Grant, Brad Johnson, Montgomery, Robbins, Rohan Smith, West