Ron,
As for those swirls and resulting issues, I gave in and did a few Google searches. I finally came up with some knowledgeable answers. 1st, the problem is very common. The less adherence to molding Quality Controls, the more issues you're going to have. In our case of plastic injected models, the sprue trees are knocked out as quickly and cheaply as possible. Hence, one of the major factoring issues.
Here's what one of the swirls actually looks like. You can clearly see that the density of the plastic is different before and after the swirl.
The greater the difference in density, the harder it is for our paints to cover it up, so we end up with a uniform and consistent painted surface. Sanding/polishing ruffs up the surface and creates a uniform surface to paint on.
What I found in my searches is that this and related problems are caused by several issues.
1-The temp of the liquification process of the Plastic pellets is to high, causing excess gases to be trapped within the liquid. In the above picture you can see the bubbles of the trapped gases.
2- To high of an injection pressure, ei. fills up the molds at a faster rate.
3-Contaminants of both the liquid Plastic and or the molds.
These are main issues mentioned in several of the articles I read. It's pretty obvious that reducing costs are a major consideration to profitability, and the results are swirls, short molded parts, & cracked parts (especially clear parts).
Joel