I think the difference is just a little bit of trim on the doors and maybe nicer hubcaps. If you go to
www.rockauto.com and put in your Neons year and model, you can do a compare between the regular Neon and the highline, and see if there are any differences in the mechanicals. I suspect there wont be any.
We have a 97 'highline', and I have had the engine out, done work on its wiring, etc. Never has the 'highline' part made a difference in getting any part for it. Our highline didnt even come with an instrument cluster having a tachometer in it - but I got on from a boneyard and installed it. Its nice to have the tachometer working when the speedometer would decide to drop to zero on the interstate.