Here is a wild thought or two - which I think would be difficult on the practical level but however have a place in such a discussion.
If levels are not important, could RP be enhanced by narrowing the level range people play at ? IE say we all play within a small range of levels say 5-10 difference between starting and finishing level?
Or as someone mentioned they have characters at different levels, so essentially a PC to fit in with different parties. This kind of supports people want to play characters around the same level as others. A lot of players here have such a mix and have created this over time.
However diminishing player base etc - should new starts immediately perhaps, or after a settling period, be allowed - say for example 20 free levels, to be shared among one or more of their characters at their discretion. (or against some agreed constraints)
Some people like to do all the growing/grinding (you don't have to take them)
For those that just want to be part of things - especially the casual player, you get a chance to roll dice and RP right alongside others on some of the big quests and are not seen as healers, loot carriers, note takers and other reasons given for RPing when you cannot compete.
There is an assumption here in this idea that a player can RP a bigger pc as easy as a smaller one. Therefore how and when you agree upon that idea is relevant to when a player could take up such an opportunity. IE if you dont think a new player should be allowed this opportunity until they have proved themselves then you would need to defins that appropriate time.
But whenever you reach that decision then playing a part, whatever part, does not diminish the effort put into RPing (ie can someone play a preprepared character essentially - or do you feel you need to earn all these levels (we often say this game is not about) to be able to play them ?
Not sure personally. But this just seemed a natural follow on thought to this thread?
You could of course assign some baggage/personal history on forums/PM that players get to play out when starting out with an accelerated PC (see I even got a name in for it)