How many were built doesn't show anything about the original intent.
The original intent was to create the appearance of a threat, as evidenced by both the plans and actual production numbers. From the very beginning, the Soviets understood that with their very weak aluminum industry and the lack of powerful aircraft factories capable of mass production of 4-engine bombers, building a large series of Pe-8s was absolutely unrealistic - in 1939, a plan was adopted to build 51 aircraft in eight production batches. No one dreamed of thousands of bombers in principle!
Again, actual production does not show original intent.
Taking into account all the circumstances - yes, it does.
The US built a number of planes with no real intention of mass producing them. The Boeing B-15 and Douglas B-19 being prime examples. But they did show the problems involved and helped refine ideas for later aircraft. The US was very interested in long range bombing. Both of these would have been failures (engine technology was not good enough for one thing) but it helped get them to the B-17, B-24 and B-29/B-32. It also helped show the US command the problems that any enemy would face trying to build planes for the same mission.
Please, don't compare the capabilities of American industry with those of the Soviets. It's not serious.
Again, planning and interest are not the same as production.
In the USSR there was a clear correspondence between priority and output, as resources were extremely limited. The Pe-8's high altitude performance was a priority, but production of this airplane was not planned in the quantity needed to produce high-altitude escort fighters for it. High-altitude fighters were not a priority. With a shortage of everything, the Soviets prioritized correctly.
Also showed what the Germans needed to do to come up with solutions. Germans came up with solutions but it took a while and carting around hundreds of kg of nitrous oxide in insulated tanks worked, just barely.
In this case, there was only one solution - to obtain heat-resistant alloys. And the Soviets got it only with captured German engines. The Soviets had difficulties with materials science - IIRC, many basic (perhaps the most) Soviet aluminum and heat resistant alloys came about after acquaintance with Western samples, starting in the 1930s.