I’m also pretty new to this so it’ll be kind of like the blind leading the blind until some bad-ass pro chimes in.
In my experience, UV’s are always going to be time consuming and somewhat of a pain. What you have looks like you just auto-mapped the entire car, which is fine if you’re doing all your painting in a 3D painting program like mari or substance, but totally unusable if you want to paint-over anything in Photoshop. You may also get a bunch of messy seams all over the place, but that depends on how the textures are being generated. Again, if they’re all produced by a 3D painting program, it may do an ok job of hiding the seams. It all depends on your standards and how neat you want things to be. Also, having lots of seams makes using any tiling textures impossible.
For production quality, there’s really no way other than to manually create all your seams by hand. There are some pretty speedy tools for doing this, like Headus or the new bonus tools for Maya. I haven’t played with Unwrella, so I can’t say a thing about it. Obviously, if you have any repeating pieces (like the tires, doors, engine parts, etc.) you can just unwrap one and transfer the UV’s to the others. There are lots of projection, unwrapping and alignment tools that will help. Nightshade is a pretty useful one for Maya, with some nice alignment and measurement tools.
http://www.creativecrash.com/maya/script/nightshade-uv-editor
As for PTEX, the downsides as far as I can see are that it only works with certain programs (mari, mudbox and a few others) and you can’t edit your maps in Photoshop because they look like total giber gabber as files. Sometimes it’s useful to paint over maps if you have export issues that you just can’t seem to solve. But apart from that they’re a pretty neat deal and I’d definitely encourage you to explore that route and see where it takes you!
Hope that helps.
