If you do the math the current won't "dramatically change" when the source voltage varies "slightly". It will of course if the supply changes from say 3.3V to 5V, or 9V or something, but is that what you expect?
A 3.3V supply is usually very well regulated, so the resistor will be just fine. A constant current driver would be overkill.
LEDs are approximately linear light output with current, so changing your current by even say 10% will have little if any noticeable effect on the perceived brightness.
Dave.