ZRM 4.5-ES/C marketed as ignition cut-off, not sure if smart enough to prevent cycling, too.

Ignitor being TOO smart is the source of its problems in practice unfortunately...

@RRK: Are the Tridonic ignitors you got, anti-cycle or regular?

I know once there was a fire caused by neglecting to use a regular not-HV rated cable from ballast box to luminaire in the case of non-igniting MH lamp! So far, so good, ask me how I got four combos of nice NOS Tridonic 150W chokes with nice NOS Tridonic igintors for VERY cheap haha!

We had a rainfall today: https://www.youtube.com/watch?v=YPjPBihIw58
But it is the only one we will have this day.

There are two types of anti-cycle ignitors:
1. One that gives up ignition attempts after few number of cycles.
2. One that monitors the lamp conditions and fires to stabilize a lamp that about to extinguish, and gives up ignition attempts after the lamp extinguished.

If they're series, a retrofit to multiple would be very costly, same goes for restoring 50something luminaires. The replacements look good!

This is indeed the general answer. A more specific answer depends on additional considerations :

Ballast insulation quality varies. Some ballasts don't mind it too much even for years, while others may be damaged

If the ballast is exposed to moisture, its insulation may be bad enough to the point where it barely withstands even normal lamp starting or plain line voltage. In this case the cycling lamp may just what pushes it over the edge

A ballast independent (superimposed) ignitor does not expose the ballast to ignition voltage, in this case the ballast only have to withstand Voc, which any intact ballast will withstand indefinitely

Ignitor quality varies. I have seen an install with 5 floodlights, of which 3 were powered full nights for 12 years with no lamps installed, continuously ticking all night long, and were still intact. (Eltam K75 ballasts and ES50 ignitors)

The worst ignitors i have seen have underrated components which can't survive the "lamp open circuit" condition for too long. In one such ignitor the charging resistor melted right out of the side of the ignitor through the plastic. This is not result of the ignition voltage, but just of it getting powered at Voc (charging the ignitor from the ballast output) for too long

Some ignitors are "smart" types that stop attempting ignition or reduce it to quick attempts with long delay between them if they figure out that the lamp is bad

The luminaire wiring and especially remote ballast wiring is also susceptible to damage from ignition voltage if there is any initial small damage to the insulation

Yyyyep. Think of the 'MAH TAXPAYER MONEY!!' screams if it comes out that it costs thousands a piece to restore it, versus hundreds to put in a new one. Who knows, perhaps it will cost even more because 3rd parties LOVE to suckle on that teat of sweet govenrment money, and you know they're gonna ramp up the prices by a factor 2 or 3 once they know it's the government's money.

Personally, i think these are worth the premium to restore because street lamps are very influential on the feel of an area, but with labor from the local government itself because i have no trust that 3rd parties will do the job at reasonable cost without price gouging.

Perhaps a vote, with a clear explanation of the cost for each option for the specific community would be appropriate? I don't know kensington but it sounds like a rather affluent neighborhood who could easily miss like 50 bucks in 'historic streetlamp tax' per family that year.

Speaking of lead paint - i just unexpectedly encountered it in a bog standard 1960s AEG fluorescent fixture. Was polishing it with a mild abrasive cleaner, then wanted to wipe away the last bits of remaining abrasive with a dish cloth. After doing that i tested it just to be sure. And welp, bye bye dish cloth.

 To restore the originals you'd have to carefully remove them , take them apart and strip them of all of the old, more than likely lead based paint , replace all of the gaskets and wiring (more than likely asbestos!)  the socket (I'd guarantee the original isn't UL rated !)All this would need to be done off site which means the community would be without lights for however long it took the contractor to restore them . Plus , what happens if you acccidentally break something ?  Add in the environmental costs of disposing the hazardous materials to the restoration cost and restoring the old would probably cost at least 3 times what new costs . 

As far as I know, a cycling lamp causes wear on the ignitor and possibly the ballast insulation if left neglected for too long as the ignitor would keep attempting to restrike the lamp over and over again when the lamp goes out. Ideally, you would want to replace your lamp as soon as possible.