Honestly these days people are much more interested in mains for pking use rather than for PvM and bossing due to slay drops like whips being dirt cheap, all hilts (except maybe arma) are too cheap, bandos is 17m a piece, dfs is ridiculously cheap, claws, the list goes on.
Basically in order to maximise the value of your account your definitely gonna want to have 95 pray with curses as a main. This involves not only the cash needed for the skill, but also a tonne of questing. Other quests people will want done are the void stares back for korasi and elite void, hand cannon, tasks for ardy cape. Basically people are interested in untradables, mainly for pking.
Oh and how could i forget.. DUNGEONEERING. People are willing to pay ALOT more for your account if you have a bunch or chaotics, ring of vigour, etc.
For your convenience im gonna throw up a list of things people will look for when buying a main:
- CHAOTICS
- Other dung rewards (arc stream, vigour, shields, prayers maybe?)
- Imbued frem rings from MA (Onyx, Zerk, Seers, Archer)
- Quest items (Korasi, elite void, SW Cape, cannon)
- Barb Assault items (Torso, Fighter hat)
- Curses (95+ minimum on a main)
- Lots of fire capes and drag defenders in bank!! (Very important when it comes to mage bank pking)
People can add to the list I'm sure.
So in answer to your question, I would sell the RSGP for irl $ and spend the time you WERE going to spend on skilling on getting untradeables instead. This will be sure to bump up your price.
GL Selling
TLDNR: Get stuff from above bullet points