the old ones were made to be abused. i have a '95 mij atk100 and the previous owner had it in a plane and when the hardcase broke. bass came out with a few paint chips but the neck was still perfect.
i've tried the new atk300s. it's lighter than the old ones and the feel is just cheaper compared to the old ones.
I had a 95 5 ATK305 - sounded exactly like my 2007 ATK305.
Here's MY experience:
2007 one is LIGHTER - love that
2007 one has satin finished neck - prefer that to the old w/ glossy finish
2007 has truss wheel adjuster - much nicer that headstock-accessed nut
2007 has smaller circuit boards and separate battery compartment - old one has battery mounted to the single ciruit board - bad/scary design IMO
2007 - my first one has a neck issue - returned under warranty for another which is great - old one had similar neck issue, found out after warranty
So my experience has been that they sound the SAME and the new one is built as good /better. It doesn't feel quite as "substantial", mostly due to lighter weight, but that is not a negative for me. I can see why some feel the new ones feel "cheaper", but I believe they are just as tough/durable/solid.
Jamie