Will a one-way ticket I buy now still be valid after the fare hike? Or will I have to pay the difference?
The reason I ask is I wonder if I should buy a bunch of tickets now to save $$.
There doesn't seem to be any answer on the MTA web site.

Q train: LIRR and MNCR tickets will be valid for six months before and after a fare increase. The penalty charge is now an average of six dollars under the new fares.
MACTRAXX

You can pay the difference to the Conductor. Same as if you have an off peak ticket during peak times. You pay the difference to the Conductor without the on board penalty charge.
Heck I've even gone to the tix window to upgrade and they tell you to do it on the train.

Actually I've been able to use tickets purchased prior to the fare hike. They are good for 6 months from the date of sale, which is what I was told.