I personally think just have VIP give you a IG currency stipend. Maybe occasionally have a monthly bonus of something minor and cosmetic (like a cloak or some stuff). This allows people who throw in with the company to actually guarantee they get something.
I suggest this because I have seen it work well first hand. The idea is it works like this.
Every month you will gain some ingame currency - but one some months you might also get a VIP reward (cloak or hat or some cosmetic item). The currency means that you will always gain something (but not at the same rate as someone buying the currency straight up - like a 90% return on your money rather then 100%) but you also are rolling the dice that there is a goodies coming to you. Alternatively if you throw in for a FEW months (4-8-12 as standard) then you gain MORE currency for $$ then otherwise (like 110%).
Example 1$ = 1 gem
Sub is 20$
So you get 18 gems when you pay
However if you sub for 4 months @ 69$
you get 80 gems when you pay
8 months for 120$
you get 160 gems when you pay
and so on.
That way your tossing money ahead for the hope that you will get what you want and have gems when you need them and as an added bonus you get the special snowflake thing...maybe a title...maybe a cloak skin or some such; just a little bonus for putting your money into the game.