Without going into too much detail I think part of the problem in knowing what 'R' type rating to place on a climb is going to depend largely on 'familiarity' with Arapiles type routes. This brings up an important point: Are you grading for the person well accustomed to Arapiles intricate gear placements, or the person who is visiting from interstate/overseas? I would suggest the latter. People who are used to dealing with Arapiles intricasies (especially with the blind type of climbing/gear finding that onsighting many of Arapiles routes demands) then for sure - some routes won't appear to be overly dramatic. However - for those not used to the rock (and that's who you have to accomodate surely) - then you will find that something like Unrequited (to use an example) will seem quite dangerous indeed.
I'm not a fan of merely giving a number to a route and letting the climber make the decision from the ground. A lot of Arapiles routes (as suggested) are complex affairs to onsight, with the gear placements not revealing themselves until you are right on top of them - or in some cases - past them. To my mind certainly some sort of symbol - not a rating - should suffice. Rock Fax have long used the 'Heart Flutter' symbol to denote routes that 'may raise the pulse factor' - something like that would do nicely. But another idea is this - and could be uniquely Arapilesian: If the route has good gear - but is the type of gear that is very intricate to place - then how about a symbol to simply indicate this? That will give the climber a choice straight up upon reading the route in the guide. Intricate placements. Yeah sure - I can deal with that. Or no - I can't, or don't want to. Obviously if the route is exceedingly dangerous (and there aren't that many of them around) - then something else is required.
I agree with SpiceLab's comments regarding Scorpion Corner vs Unrequited - and there are so many other examples that beg for this type of differentation. Compare the likes of Starless & Bible Black to Los Endos; Missing Link vs Mari; Down & Out vs Dazed & Confused; Tannin vs Rats Alley - the list goes on. Plenty of people (not accustomed to Arapiles) have absolute knee-tremblers on Missing Link (I remember one UK climber years back even suggesting that it would be E3!) - whereas others find it to be absolutely fine in terms of gear. But who are these people? 1 could have just got out of the car from Sydney - never been to Arapiles before and wants to do a 3 star classic 17 that's world famous - the other might have been living in the Pines for 6 weeks. The experience is going to be totally different.
All that said though - it's obvious something is required to make such differences known - and unless you conscientiously make the point within the route description (something that hasn't been uniformly adhered to in the past) then a symbol must be the easiest solution.