If you have no status or some form of upgrade instrument, your odds of getting an upgrade are pretty much zero if you don't ask for one. If you ask, your odds are 0 at worst, but there *may* be an off chance that they are oversold and need to bump someone up and it doesn't hurt to ask if you could be the lucky one.

I agree it might be a bit annoying for the agent, but asking for one certainly doesn't mean you feel entitled to one.

I rarely ask for an upgrade but have received upgrades from Y to J twice just by asking, both on AC YYZ-LHR. Once I was travelling alone and knew the flight was oversold (no status) and the other time there were 4 pax in J and two in Y (couldn't get J tickets for the other 2.) Asked at check-in - were willing to pay - but were given one J seat for free. There were no more J seats left so one pax had to slum it out in Y.