Why the heck do people 'assume' that new exploration is to be done on new planets alone?
Please.
Most of the exploration is conducted in deep space, by observing numerous stellar phenomena and not just encountering new civilizations.
This is something that's been established throughout various Trek shows.
To have your 'adventures' be set on 'planet of the week' would end up rather boring for me.
I much prefer stellar phenomena exploration, plus aspects of the universe from 'where no man has gone before'.
That's the kind of exploration that you cannot really do with transwarp beaming.
Unless you decide to transport the full ship and it's contents to a specific location and let it do it's thing.
TW beaming can be very effective and useful, however I do not see it replacing starships anytime soon.
Furthermore... we have to take into account it's range (given it's TW beaming, my thought would be that it would only be a matter of time before the signal can reach the destination and then you can materialize whatever it is you sent there), whether or not it can penetrate shields, etc.
It's quite possible the TW beaming would in effect have an extremely long range and would be on par if not better than what the Dominion demonstrated, or for example the 'translocator' that Voyager encountered (still that was just a transporter with a range of over 10Ly's ... with capacity for transport diminishing the farther away the signal goes).
It's possible that TW beaming as such would go around all those limitations (even shields - at least at first).
But beyond beaming your away teams to distant planets, if you'd eliminate ships, you'd be stuck on the planet itself (which seems stupid if humanity is about space exploration and not planet exploration).