If your revolver's barrel is aligned spot on (not "clocked"), if your barrel / cylinder gap is .004" - .006", and the revolver is dead on accurate - I would leave the barrel on. It would be a bit more of a pain in the butt to get that high polish you desire, however the more important issue is your barrel won't be disturbed, you won't have to build a special vise jig to remove it and no possible damage can occur.
There are not many barrels that are installed with perfect spec's these days, so if your is - I'd opt to not touch it and work around it. If it's not, then you have less to loose I suppose.
I have polished a few Stainless Revolvers with the barrel on and yes it is a bit harder but not too much of a big deal that I had to remove the barrel. I did not put a mirror finish on any, I just basically restored years of neglect and minor scratches. They came out very nice!
If the revolver is sent out, you risk theft, damage, loss, and of course would incur shipping charges back and forth (more expense). Today, the "Factory" has been hit or miss as far as people's satisfaction and quality is concerned. Polishing is something that I deem a non-necessary reason to be sent out - but that's just me. Your gun - your choice!
One final note: When that mirror finish is put on, it is next to impossible to keep it perfect! Mirror finishes show minor defects and handling marks much more than satin finishes do and IMHO it becomes sort of a maintenance headache if you want to keep it looking perfect. That is of course if you are actually going to use and shoot it. Not as much if is is going to be a Safe Queen or display gun.
