A big club with no money whatsoever and incapable of keeping important players such as Nacho Novo. As it's been stated, Rangers is a big club because of fan base, and not because they're able to attract great players through money and win competitions. it was quite well illustrated this summer when Man Utd paid more for a completely unknown player (Bebe) than Rangers has spent for several years now. How can they compete with that? The Big Four to the Old Firm are what the Old Firm is to the rest of the SPL.
Rangers have bought only a few players the last few years, and Rangers have been incredibly impressive, much thanks to Walter Smith, just look at the league last year and the Europa Cup final. When you can't attract or keep talent and key players(e.g. Danny Wilson, Middlesbourgh (sp?)), you've got to try to make the best out of your squad using tactical approaches. Rangers knew very well what would happen if they opened up; just look at Celtic's last visit to OT when they opened up - a 3-0 thrashing. The Old Firm are simply not as good as the biggest teams in Europe, and Walter knows this, which is why he plays "negative" football against stronger teams (or look at when Walter or McLeish were managing Scotland). And for the Old Firm the money from the Group Stages in the CL is incredibly important, just look at Celtic's finances now, where imho a far more conservative fiscal strategy would be a lot sounder than going into debt.
Essentially,not many clubs can go to OT and carve their defence open and take the game to them. The last time a Scots club did that was back in 2006, when Celtic went to OT and lost 3-2. And expecting a club who has no money and has lost many of its key players to do so is pretty arrogant.