...It isn't intelligence that leads to technological development; its intelligence + experience. Each generation builds on the knowledge of the previous one...
I'll add to that: it's intelligence +
tools + experience.
Tools are the most important, and within that term I include methods such as maths and science, not just hammers and levers.
Cognitive intelligence is, in my opinion, largely based on the ability to 'rehearse scenarios' in the mind (thought experiments), and those scenarios can include selected memories.
For instance, many animals use simple tools, but none, even chimps, are capable of taking it the next step to wonder how it could be made better. When it wants to winkle ants out of a tree, a chimp takes a stick, bites off the leaves, and then uses it. But it never keeps a well-tried stick for next time; nor is it very selective in choice of stick.
I wonder if anyone has worked out the limit of intelligence of humans. Technology is going through the same evolution humanity has, but at a quicker rate because of having human intelligence behind it. I reckon intelligence in human must still be increasing (though stupid people seem to actually breed more) at its regular evolutionary rate, but that is a lot slower than technological evolution. From that I guess we can surmise that the must be a point in the future where technology evolution will slow and probably end up matching the rate at which human intelligence increases (assuming it still does). From that, we must be able to work out in theory the limit of humanities technological advancement, at least theoretically.
Insofar as intelligence is very much based on memory, there is probably a storage limit. Processing power is not easily measurable, especially as we're delegating a lot of it to external machines these days.
There is no reason at all to think that intelligence is generally increasing or decreasing. It can only do so under natural selection, and we have no real idea what its physical basis is, nor can we know what selective pressures are at work. Our basic intelligence is good enough for us to continually refine our tools through the basic processes such as maths and science which we have already developed.
And by the way, that to my mind is another argument increasing the odds against ET intelligence. It might be that human intelligence is not the only possible type, and that others have never come up with science and technology at all.