If you want to economize I'd say that you'd be best at keeping not pace, but the same effort all along. If someone states that you should be running faster at the end, the question would be: to what aim?
In my experience the key is to do proper training to get familiar with which is your own real long slow distance (LSD) pace. (This also applies for ultras.) It's the mind frame of not trying to push harder than you can, and simply setting to what you already know you can get to with your training. If you can or should sprint at the end of a race seems optional, but mostly arbitrary. In any case, a rule of thumb for most experienced runners is: don't overtrain.
I ran the Buenos Aires Marathon a long time ago, in 2004, and I did not try to speed up at any time. (Noted, I did an awful time, but still) It was my first marathon and I felt perfectly at the end. I just ran as slow as I could and leaving it flow as the time passed. I did my first half of the race in about 2 hours and 20 minutes. After that I just kept going completing the next half in two hours. So, yes, I did run slightly faster at the end but without no rule imposing that on me, it just came because I felt well to run faster at the end, but I wouldn't have done so if I was tired.
Just to support my argument let me wrap it up a bit with my own conclusions.
Effort is more easily measured by your own bodily sensation, more I'd say than looking at your pace in a gps watch that checks your pace. Depending on your age perhaps a HRM is an intermediate device that may be mandatory for you, and is closer to "natural perception". I'm more for natural perception, but each person has their own favorite ways of measuring state of health and mind during training/race. You can pick your own tailored way after reviewing many different strategies. No need to get into the obligation of doing one certain way because someone just said so. Trail and error.
Also, you may find useful to see other references, for other arguments, some perhaps different to my own. A simple online article states that you shouldn't run beyond your Brain-Body potential / Listen to your body, a good reference recommended by Peter Larson.
On yet another note, I'd suggest that you look for the classic opinions on the matter. I'm reading the bibliographic material from James Fixx's book The complete book of running. He points out that one of the first to intoduce and tackle the LSD subject was Joe Henderson with the 1969 book Long Slow Distance: The Humane Way to Train.