When is using a suspension fork worth it? I've recently picked up biking again since my childhood years, so I'm quite the newbie. I've figured out most of the features I'd need so far but I'm at a loss at this one.
Why would you pick front suspension?

In my case, I'll be commuting 5 miles each way every day, 1/2 through paved road and 1/2 through gravel trails with a ~200m stretch of moderately bumpy off-road.
Proviso - my advise presumes you are not looking at forking out $2K or more for a bike, and probably significantly less. At a high price point I might suggest suspension. I also presume the gravel section is well maintained with average (pea - grape) size gravel (Where I ride, we sometime use logging roads, the "gravel" is stones about 2"-3" across.), and straight rather than technical single track

Advantages of suspension - Softens the ride on the arms making the ride more comfortable, holds front wheel on the ground providing better handling, especially  while cornering. Allows you to ride a straighter line than you might otherwise be able to. 

Disadvantages: Heavy and very expensive for good shocks, need maintenance and cheap ones don't really work well. Absorb energy while riding slowing you down - can be mitigated with a lockout, but even ones with lockouts move a bit. 

You only have 200m of rough ground to cover, so a suspension fork is probably overkill. If I was buying a bike for that commute, for the same $$$ you will get a significantly better bike with no shocks, any loss of time over 200m of rough ground would be made up on the rest of the 5 miles because of the better quality bike. Cheap shocks won't really help with the comfort, so unless you can get to at least a mid range in price, don't bother.

I would consider padded hand grips and gloves - cheap and easy to "tweak" if needed. Also big tires will help with the rough ground and gravel - I would look at 1.75"-2" slicks, and probably a 29er MTB of cyclocross style wheels (depending on your height).  

Consider a quality steel frame if you cannot afford carbon - they absorb vibrations much better than aluminum. The problem is many shops do not stock, and know nothing about steel and will tell you "stories".