In the context of the second movie, it wouldnt have made much sense to keep it the same.. Speaking from a Marketing standpoint anyways..
They were a business that was essentially reopening as well as expanding during the second movie. The public has expectations as to what a business “looks” like, especially when it expands.. The public sees an updated sign and and updated car as Progress and it reinforces the impression that the business is doing well, and it therefore reliable and worthwile to hire. Take a look at some of the businesses around your area that use vehicles.. How often to they update their vehicles? How hard do they work to keep the cars and trucks they use looking nice. Bak in the world of GB2, the updates made to the car make it look as if they have expended and enhanced the capabilities of the car. Its all about marketing yourself. They did commercials, they got a new logo, they upgraded the car.. All to present the image that they were back, and bigger and better than ever..
The general public is attracted by Bigger and Better.. The Ecto-1a “looks” bigger and better than the previous version did.*
I think its good that they put enough thought into the little details to make the changes that they did. So many movies completely ingore realities and create a totally fantasy world and then expect us to believe that its just like the real world.
Also, from a “real world” perspective, a New Ecto Version would allow the Studio Marketing guys to market a whole new bunch of stuff for the movie.. (New Toys, Shirts, Posters, etc)
*Personally, I like both versions, so I'm not saying that one or the other is better.
Just my Thoughts..
TheEcto1a