While on that note, I wanted to ask, anything made out of resin has no openings (i.e doors trunk etc), correct? Are they more valuable and/or more expensive than diecast? What other brands besides autoart, norev, solido, minichamps make models that has openings? If I'm looking at more premium models, is there a distinct ranking on the brands based on the quality and details of their models?
I am not an expert on the hobby, though I've been collecting for maybe 15 years so I'll take a stab at answering as best I can. Disclaimer: I only collect Porsche 911s so my experience may be skewed.
Resin models are generally sealed models, but I believe there are a few opening ones, just as there are some sealed metal/composite models. Are sealed more expensive/valuable? Well in my opinion sealed models
shouldn't be more expensive no matter the material used to make them. The hobby has seen a spike in "premium" sealed models that carry a big price tag in recent years, such as Spark, but there are still some good budget options out there.
Sealed vs opening is a heated debate in the hobby. As you'd imagine many collectors prefer the option to open their cars to see as many details as possible and to get their money's worth. Some people may view sealed models as overpriced with less details and refuse to collect them. Others see sealed models as a, sometimes, cheaper alternative. I personally do not have an issue with sealed models, when the prices are reasonable. However, in most cases the sealed models I do buy are "place-holders" for eventual (if ever) opening diecast models to take their place. Right now my collection is almost exactly 50/50 sealed and opening. I may be in the minority, but I collect the cars I want, regardless of quality. With the cost to develop/ manufacture a sealed model vs opening, you'll likely find that obscure and unique cars may never be made in opening form, so brands fill the gaps with sealed ones.
There are brands that make opening models other than the ones you mentioned, but many I do not have first hand experience with. Off the top of my head some I hear are good are Almost Real and MotorHelix. Kyosho is good, too. These ones are high priced, but high quality based on reviews I've read. In fact, MotorHelix might be putting out the best stuff for the money, so I hear.
Some brands I have experience with and my opinions:
Autoart is a good benchmark, think they make some of the best models for decent prices still. They've also moved to a composite material rather than metal.
Norev I will place slightly below Autoart in quality these days believe it or not for a lot cheaper. Currently my favorite brand.
Minichamps is heading in the wrong direction, I say. Their models are getting more expensive and can't necessarily match even Norev in quality.
Schuco used to make great opening models for cheap, but they have been bought out by Spark and make sealed models now, and not cheap ones.
KK Scale makes sealed models, but not bad for the price. They seem to be improving in quality too.
Solido makes surprisingly decent models for cheaper than nearly anyone else, but only the doors open on their models. Still better than sealed, perhaps.
Maisto still churns out extremely cheap models but they never seem to dip in quality. They certainly are a good place to start collecting 1/18, I think.
Spark makes very expensive sealed models. They are good if you can get them on sale or at least retail as they become a bit too costly second hand.
GT Spirit/OTTO make some of the best quality sealed models in my experience and usually not bad prices.
