On e.g. the Saturn and Shuttle launches, vulnerable items like umbilicals are retracted into closed spaces, with a door closing over them in time to protect them.
This very detailed video of a Shuttle launch shows some of those (at 9:40, for example).
The audio commentary mentions (around 9:00) that the cameras on the platform and tower are inside explosion-proof boxes, in a nitrogen atmosphere. The lenses are protected by quartz glass covers. These get damaged sometimes and have to be reground and polished.
On almost every launch, items like tools were left behind and got blasted away, melted or otherwise damaged by the rocket exhaust. Even parts attached to the tower structure sometimes get blown off. NASA does a post-launch inspection after every launch.
The entire tower is designed to explosion-proof standards.
They typically spend a few weeks making repairs, re-painting rails and other sections that have been stripped of their coatings by the launch.
Everything has to be painted to prevent corrosion in the salty sea air at Canaveral.
The concrete of the flame trench has been known to need occasional repairs too.