...Did a lot of satellite maintenance every occur?...
Do you remember the classified Shuttle missions
with only military crew members? They were refueling Keyhole birds. (Allegedly, Keyhole12 (aka Misty?) and it's decendants are refuelable) Money may be saved by having the capability to refuel sats built for long service life. One Keyhole sat costs about what a modern aircraft carrier costs: $1 billion. It is definitely cheaper to bring up some more fuel than to design, build and launch another billion dollar satellite. We've been plodding in this general direction for years. Decades...
How many times has
just the Hubble been upgraded? Many times.
For some time now the US has been trying to standardize two things: refueling ports on sats designed for refueling by an autonomous ship and bays for sats that will accept upgrades in standard form factors, again, to be delivered by and swapped out by autonomous ships.
It's all a very big deal. If they screw up on the design and the sat is delivered to orbit Dead On Arrival or just Fuzzy On Arrival (like the Hubble was) it's a great time, money and face saver to be able to have the tools to fix it. Also many of our sats have service lives long enough that upgrades will be planned even far before initial launch.
There was a program called
NEXT (for Next Generation Sat). Unfortunately, I no longer remember the name of the second half of the program.
Along these lines we also have a sat delivery bus. Once loaded onto the bus, sats for more than one destination may be launched into a parking orbit for a few days of post-launch testing before final autonomous delivery to their individual stations. The bus will deliver multiple sats much more cheaply than using two or three stages for each.
Previously our only course for refueling and repairs/upgrades was the Shuttle. If we did not see these very same abilities live on in other systems we would have
never retired any Shuttles as long as we had some still flyable.
My own conclusion is that this is a very versatile ship.
The X-37B already far enhances the capabilities of the defunct Shuttle in regards to upgrades and refueling. And even the ongoing developmental costs of these types of
unmanned ships are dirt cheap when compared to flying Shuttles around. Of course, having the ability to do meaningful work way, way,
way outside the Shuttle's confined environ within NEO is what really makes this thing cook...that and all the black stuff inherent in a vehicle with the range and endurance of the X-37B.