There is something of a Remote Race community here on the forum. Truth be told, if you had 3 level zero drivers online to share and were willing to reciprocate, the Remote Racing will soon bump up the Levels, so there is no harm in maxing out at 6. Maybe keep a couple offline for your personal use if you feel you need to.
I had level zero driver jump to around Level 23-25 overnight by being Remote Raced by an online friend. I guess, only guess mind, that some would say bumping up like this isn't technically YOU earning the XP and I would agree. I kept my boys offline thro most of b-spec and just tried Remote Racing when I fancied a change. The money, which can be considerable, is nice though I haven't really been short of money in this version of GT, so isn't everything. Useful if you are skint though.
Hope that helps