I think it depends on several factors, but ultimately I see conversion as a good thing.
Just to start with a couple of base assumptions: First, wooden coasters don't age well. I've read many memorable threads in here describing bad coasters, and bad woodies tend to bring out the poet in people, usually alongside their lunch, by way of vigorous shaking. "Made me feel like a squirrel strapped to a jackhammer", "Feels like it tried to shake my spleen out through my nostrils", "My back felt like my spine had been reshaped into the letter K", or phrases like that tend to emerge when people describe the experience of riding woodies that haven't been maintained that well.
Second assumption: Wooden coaster maintenance tends to involve swapping out a lot of bits in the off-seasons. Elements under little stress and few dynamic forces can stay in place practically forever, like pieces of the lifthill structure, but turns and valleys need to have their wood replaced every few years. That's not to mention how pieces of the trains, the brakes, the lift hill motor or the control system will have to be periodically updated as well.
These two things together mean that change is inevitable for a wooden coaster in operation. Age itself will change the ride experience, and keeping the ride in shape means that its physical parts will have to change instead. In other words, perfect preservation is impossible, or at least incompatible with continuous operation.
That leaves the question: What, exactly, is the park trying to preserve? The ride itself or the ride experience? As the former is an impossibility, we can define the latter as "not making significant changes to the ride's design", or swapping parts like-for-like. This would of course be done as part of regular maintenance within the coaster's life span, we're only talking preservation if the ride has aged to the point that major refurbishment is in order and the park still chooses to uphold the original design.
I think that preserving a ride like that in the long term should only be done if the park feels (or is given) an obligation to preserve the coaster for historical reasons. We're talking about the likes of Grand National or Coney Island Cyclone. The kind of preservation that makes the park eligible for public funding for the preservation efforts. If the ride's expected lifetime is over, and it's not being popular with the guests any more, I fully understand if sticking to the original design isn't the most preferred option. Bring on the re-profiling, the Timberliners, et cetera.
In the case of RMC conversions, which I think is more controversial to many, I'd ask: "What is the alternative option?". If the park has an unpopular ride that takes a lot of land, requires a lot of maintenance, has no historical significance, and a refurbishment would only restore it to working order (but not give the PR boost of a new attraction), I'd say its days are numbered in any case. Coasters like Twisted Twins or Gwazi were decommissioned and taken out of operation already before RMC came a-knockin', and I think some of the other converted coasters could have been headed for the same fate if not for the RMC option. For instance, SFGAdv removed Rolling Thunder, SFMM took down Psyclone and Carowinds demolished Thunder Road, without any direct replacement. Track re-profiling and new trains could only take those coasters so far, and the park apparently found it better to clear the land for future developments. In such cases, an RMC conversion would simply be a shortcut from the closure of the woodie to the opening of a new attraction. If the woodie is going and a new attraction is coming anyway, one might as well build the latter using parts of the former. It's also an excellent way to keep the memory of the old ride intact, as people can say "I remember when this coaster was called Cyclone" instead of "I remember when a coaster called Cyclone stood where the Sky Rocket II and the burger bar is today".
TL;DR - Woodies are great for a while, but they do age, and at a certain point they will need an overhaul. Keeping the ride as-is is rarely the most profitable (or exciting) option, and unless the park wants to preserve it through refurbishments or new trains, it will probably get knocked down anyway. In that case, an RMC conversion will at least be a quick and resource-efficient way to build a new attraction on the same land. Preserving the ride according to the original design is the rarely used third option, not the default, and should only be done if the park or public particularly care for it.