There used to be a bug where you could simply use the same 10 darts over and over but that was fixed a while back. When it was working though this was the way to go even though the timer is three minutes verse every 32 seconds on the regular bows. I was using several temp accounts each with 10 bolts thus was hammering out 3 to 4 quests every three minutes but I never had to leave to restock. This equated to faster results and was scalable to large numbers of accounts.
Now that this bug is fixed the numbers just don't work out. Consider TM's estimate of 32 seconds per quest and each quest taking approximately 80 boards at 100% success (I think it's 8 boards per bow) this means you would run out of stock after every 24 or so quests (1600 boards on a beetle, 300 in pack) thus every 13 minutes you leave to restock. Assuming the restock takes what, roughly 2 minutes at most, you are averaging approximately 15 minutes for 24 quests verse 72 minutes if doing the bolts on a single account. This alone increases your odds of obtaining the ever-elusive Heartwood runic kit by about 78%!
There are definitely still reasons to do bolts though. It's safer because you leave a lot less often and can stay hidden for long periods of time without your beetle showing up, etc. This means less chance of getting paged on. There's also something to be said for the quest sounds happening only every few minutes verse constantly - ie, less noticable.
So I guess, as with real life, it's about risk verse profit. The riskier you are willing to be the more money you eventually end up making. Nothing wrong with a "safe" investment though

XII