Hmm...dont think it's a fad.
Most restorations I read about, and the one that I personally was involved with, share many of the same core features:
1. Reclaim green sizes that have been slowly shrunk by mowing practices.
2. Tree "remediation". Or, as we framed it: "Trophy tree preservation". (Also known as "weeding your garden"..;-)
3. Mowing line modifications.
4. Bunkers, bunker sand and drainage (bunkers do break down over time)
5. Irrigation enhancements (these systems do degrade over time.)
6. Of course, you can also build new greens or re-grass, too.
Yes, I think much of this can be handled "in-house".
BUT...given what is at stake, it is often wise to retain a GCA for many reasons. If your super can do it, then great.
It's analogous to living in an old house, which we do (1908).
In our house, we have to: put on a new roof, replace some windows, tuck point the brick, paint wood trim, replace HVAC, etc.
Old houses in our (north side of Chicago) neighborhood are getting 1) torn down and replaced by new construction and 2) getting "gut rehabbed" on a regular basis.
So are golf courses.
Some restorations are more intense and significant than others depending on how they been kept up over the past few decades.
Plus, at the more exclusive private clubs, there is a "restovation" quasi-arms race. The game has growth issues, so new courses are few and far between and a bifurcation is occurring. Low-end private courses are struggling, turning public or dying. High end courses are spending moneyand restoring their courses to maintain relevancy to new members. Plus, they are upgrading (gulp) club house facilities to attrct the elusive millennial member. (Could riff on that but I will stifle myself.)