Aluminum forks vs. carbon forks (with aluminum frames) what are the trade offs? The all-aluminum frame bike will be cheaper.  The aluminum fork should be more robust and less prone to breakage.  The carbon fork will be more shock absorbing and comfortable.  That's kind of how I see the basic trade off.

Given that I like to ride a touring bike with wide tires (25 to 28 mm) and I use low pressure, I am wondering if I would feel any comfort benefit at all from the carbon fork.  And, should just go for the aluminum one.  

Is that how you see it?
What is the make/model of the bike you are considering?  It may help in answering your question more pointedly.

There are all carbon forks (which are very expensive), and more commonly, carbon forks with carbon fork arms and an allow steerer tube.

I think you will find the carbon fork much, much better in terms of weight, performance and comfort compared to an alloy fork.  Most entry level road bikes ($700 and up) from the big brands come standard with a carbon fork.  Road touring is more or less the same.  I have an older Specialized Secteur which has relaxed touring geometry and some touring affordances.  It came with a carbon fork and I wouldn't want to ride it without one.

As far as durability, it all depends on the built quality, but I think you'd have to try pretty hard to actually crack a carbon fork while touring.  I've hit massive potholes and never damaged my fork.  I've blown out a lot of tires but the fork remains in tact.  They are very durable.  I'd be more worried about my alloy frame failing from fatigue than my carbon fork.  

A touring consideration, If you want to mount racks or fenders, you need to make sure the carbon fork has eyelets or some hardware to do so.  It is not advised to use p-clamps on carbon forks.  

So, if you can afford it, I wouldn't think twice.  Get the carbon fork.  It will steer and handle better, be lighter, and you can pick up the front end of the bike easier (like when hopping your front tire over obstacles to avoid impact).

For me, once I put some carbon on my bike, I usually and up wanting more carbon on my bike.  It just has really suitable characteristics as a bicycle material.