3M Hand Glaze will make the paint look great...I'd avoid decals...but works very differently than waxes or polishes. Glaze doesn't "feed" paint. Once paint is dry...it's not going to take on any "nutrients". Glaze stays wet on the surface and makes it shine as well as hiding imperfections. Problem is, a couple washes and it's gone.
I'd also avoid anything abrasive until I tried less invasive methods. Turtle Wax makes a product called Colorback that's not abrasive. While I prefer Duragloss, Zaino or Klasse...this works very well for oxidized, orignal paint. This is a van that we went over for a friend.
http://mattmorrisresto.com/RoyVan.JPGIf indeed it's determined that you need to compound or polish, then start at the least aggresive side. Meguairs makes a Dual Action Cleaner Polish that may fit the bill.
