Newer is definitely not always better, but newer once the bugs get worked out is almost always better in some way that is significant if you're really competitive and the people around you are closely matched. We generally call it being "off pace" when some game changing thing comes about and you can no longer catch your buddies. There are clear exceptions to this rule -- for example, the losi 1/10 4wd buggy situation, but other than that, most newer generations of offroad cars have some significant design improvements.
When the b4.1 long chassis came out, depending on the track, you would be off pace if you did not have it.
When the super soft compounds paired with closed cell inserts came out, if you did not have it, you were off pace. (I personally tested open cell vs closed cell and found 1-3 tenths a lap in difference).
When the b44.1 came out, it had some better parts, but the longer chassis wasn't really a game changer for most. When the b44.2 came out, the big bores were a big improvement for specifically that car.
IMHO, when AE big bores came out in 1/10 land, they didn't help stadium truck much, they really initially hurt buggy until we did some serious setup searching and had more piston options, and they really helped the b44 platform.
When the RC8.2 came out, it was horrible. We drilled holes in towers, used old 8b parts, purchased different sway bar kits, rear hubs... man, an 8b was way better until we figured that platform out, but it eventually became better than the 8b.
Every kyosho platform update has some serious improvement in durability, but they tend to back track on stuff like rear end setup. In RB5 land, it was really tough to keep track of which rear arm mounts, arms, and rear shock shafts were the best combination overall, and each revision of the car had different ones, and the latest version wasn't ever the right version. Same with the RB6—everyone runs rb5 rear arms now! Having said that, the rb6 is worlds better than the rb5 now that some good team setups are available.
Here's the bottom line. Each update to a platform usually includes a lot of improvements in design and a few steps back in minor areas that can make the car not as good as the previous model until all the bugs are worked out. Once the bugs are worked out, it's better than the previous car by a meaningful amount, especially if you're competitive. If you're one of those people who can't figure out the issues with the initial platform and work around them, or doesn't want to, hold off on getting the new platform till its been out a while and has settled down. Otherwise, get the new platform and start contributing to the community with your findings.