Is the Last Record Preservative system a worthwhile investment?

I swear by it.  Have used it on many of my records since 1967 or so when it first came to my attention.  First I clean the record using LAST cleaner, then apply the LAST solution.  The results, particularly on new records, is to completely eliminate high-frequency grunge on dynamic passages, if any exists.  I have records, including some used frequently as test records over the year, that still sound as new.  FWIW, I also used LAST stylus preservative and my AC-2 is still going strong.  Same principle as the record preservative.  I'm not sure it is still sold.

I have noted that the LAST record preservative I bought most recently seems to evaporate more rapidly than back in the old days.  May have been a formula change along the way.

I clean stylus with Lyra stylus cleaner before each play. I think, the smallest bottle of the LAST was enough for 50 or 60 records but I didn’t count, so it’s $1 per record or less, almost like nothing even for me.

Been using both LAST and STYLAST, since they hit the market. Bought my first VPI RCM, about the same time (a 16 and now I own a 16.5) . Never have seen the first sign, of anything gathering on a stylus. Never experienced the first problem, regarding my records. The ones bought back in the, "Golden Years" of vinyl, still sound excellent. Some were played repeatedly, every business day, for years, to demonstrate my systems. Always clean(ed) and treat(ed) them, before the first play. Just another happy camper!

Yet another happy user since 1982 here.  I can't say that it improves the sound quality, but it does drop surface noise near to the limit of whatever the vinyl material can deliver.  That might seem like it improves the sound simply because the S/N ratio is maximized.

I have found LAST works quite well on all the vinyl I've purchased pressed from ~1955 to the present.  As others have noted, the key is starting with a clean, dry surface.  If the vinyl is new, I use the LAST Power Cleaner (mold release remover) first, then I use an ultrasonic cleaner with distilled water and a splash of LAST machine cleaner solution for everything, new or used.  Another wet clean with LAST cleaning solution and my trusty Discwasher brush, a thorough dry and then the surface is ready for preservative.  If you've gotten everything right, you can actually feel the preservative bonding with the vinyl while applying it; the brush seems to move with less friction. I'm sure that's due to the molecular effects visible in the micrographs referenced above.

FWIW, I've also used Stylast and the LAST stylus cleaner since they became available.  I've never identified any audible difference, but I can say I've never worn out a stylus.  The magnets have gone south first.

From my perspective, a good value proposition for a modest investment in happy listening.