One of the things I'd dearly love to see in lifetime is a return to the ice giants (ie Uranus and Neptune). We've only visited once and it was in the 1980s with the limited tech of Voyager 1 and 2. Think of what we could learn with a Cassini-level mission and Cassini itself is now ~14 years old.
But these missions take a long time to develop. We actually have a launch window coming up in the early to mid 2030s where we could feasibly reach the ice giants but the development period is so long and no proposals are at an advanced enough stage that we've likely missed it (which makes me sad).
> 2. a much cheaper Webb telescope
Would we make a cheaper version? Or would we take the opportunity to make an even bigger version? I suspect the latter. And JWST took 20 years to develop.
> 3. build a base on the moon
I actually believe we'll see a man on the Moon in the next 20 years. It could be much sooner but these are still government programs subject to change at any moment. I mean think where we could be if the SSC had been completed.
Apollo was driven by Cold War era competition. Our appetite for risk has changed. This means we may not see a Moon mission until rescue in the event of a catastrophe is actually possible. That will delay things.
> 4. make a mission to Mars possible
There's a thread about this from earlier today. IMHO a manned mission to Mars makes almost zero sense. Despite Musk's wildly infeasible and impractical predictions about Mars colonization, I wouldn't be surprised if we don't see men on Mars before 2050.
All of the things you've listed here though aren't really commercial enterprises. Or at least they're far from it. They're flagship missions by governments because they're so wildly expensive. This creates some demand but is it sufficient to justify the program? I don't know.
I do suspect we need to find commercial enterprises to justify the Starship economics and I'm just not sure what that looks like yet.