Yeah, after thinking about this for awhile I must agree. I've even started a new playthrough just to challenge my own past experiences and assumptions, and I must say that you're completely right that facing potential roadblocks all the time while exploring would probably spoil the experience to some extent. Actually, now that I think about it I feel like what started my initial thoughts about the matter was probably more related to the variety of exploration-related encounters. As stated before, I feel like it all really comes down to adding new and varied choices for the player to make and encounters to experience, not simply making the grind longer/more annoying. That's also why I think making procurement missions harder isn't really necessary in this context. Having a safe but a bit more boring option for progressing isn't really a bad thing. Maybe the rewards should be a bit more balanced to make this way of progressing a bit more streched in time, or as you've mentioned adding some sort of sporadic blockades that the player would need to sneak by/fight trough would also be an interesting idea. Actually, when thinking about it I really feel like most of the currently present activities could potentially benefit by being expanded like that, without necessarilly making current variants more difficult, but by adding new, more complex (and potentially rewarding) ones.
Going back to the topic of exploration, I feel that it's not like all the rewards need to be locked from the player in one specific way. Well, thinking about it I feel like there's really nothing wrong with the player accidentally stumbling upon some amazing treasure troves by pure chance and accident. As you've said before, it's not like the world itself (not talking about [Redacted]) should really feel like it cares whether it is explored by the player or not. I just think that it would be really nice to have some new types of encounters while exploring, both threat/fighting related and not. For example, addition of more "passive" type of gatekeepers, on top of more "active" ones, like some kind of access codes that you would need to found while exploring other systems or by talking to other explorers in bars would make an excelent way of making exploration itself more varied, without making it necesarilly simply more difficult . I think that the example given before by Morrokain sums it up pretty well. There already are informations about locations of caches and ruins that you can stumble upon while scanning probes and derelicts, it would be great to see this system expanded even further. At the end the player is not the only person going on this expeditions, having a possibility to find a bankrupt explorer in a bar, ready to sell some vital information about some of his last interesting finds would be a nice, very natural possibility to have, adding a new layer to exploration gameplay. Of course, I'm saying that as a possibility on top of all the other ideas that we all came up with during this discussion.