For the mean-time, he is best staying.
For example, he is a part (albeit not a huge part) of an exceptional team. Messi, Henry, Eto'o.....If he is going to learn anything and anywhere, it's from those three and at Barcelona. His situation in some ways reminds me of how Iniesta made it in to the team. He stuck at it for a long time, taking advantage of every substitute appearance and rare start a few years back, and look at him now. I'm not quite sure if it will work out the same way for Bojan due to obvious differences in ability and position, but for the time being, he can do no wrong in being a substitute at the age of 18 behind the likes of Henry, Messi and Eto'o in one of the biggest clubs in the world. Going on loan I feel will only ruin his chances to impress in training and on the bigger stage when he gets the chance.
One other point though. These links with Aguero and Benzema don't look too good for Bojan's long-term future, but you never know, I hope he progresses well enough to get into the team eventually...