[quote=@BangoSkank]
"what does success mean for me as a GM/RPer"
[/quote]

Because I'm petty, I'm going to answer my own question, I'm also going to quantify my answer as I feel that makes it a bit more practical.

As player success is completing a character sheet that I am happy with.

I consider it a bonus and view an RP as extremely successful as a player if I manage to make one post in character before said RP dies.

Although I don't GM, if I did GM I would consider a group RP as successful if I got three players to submit character sheets. If each of my three players posted once before my RP died, I would consider my RP to be extremely successful.

Finally, although I will never 1 x 1, if I did 1 x 1, I would consider it a massive success if one person expressed interest in my ideas. Getting a 1 x 1 to the planning stage would be even more of a success and getting one post each into a 1 x 1 would in my book lead me to consider it successful.