So are you referring to the main product title or the meta title or both ? I guess I could use all my sparkling type words just in the descriptions ?
Referring to both the {{ product.title }} and the {{ page.title }} - keywords placed in both is generally good for SEO. Putting some glitzy brand terms (that no-one searches for) in the description as part of copy to make it sound good and entice a click (within 160 char not 320) seems ideal. The {{ product.title }} and {{ page.title}} will have more of an impact on SEO. The description text is not a strong SEO signal.
Again this is all from a purely SEO sense, not considering how you want your brand to look! Also, I have only checked one product, at a very surface level, with out any other context. I’m just spitballing ideas on the info I have at hand. My typical process would be a LOT more strategic and based on much more thorough keyword research before making a definitive recommendation like you are asking for.
If on the other hand you are an established brand like Nike, people will probably search for “Nike mens black shoes” so in that case you probably want your page to be titled “Nike mens black shoes”! But if no-one knows your brand already then the only real SEO play (right now) is category terms. It’s all based on what people are searching for, how this fits your brand, how this fits your product and constructing a titling/naming convention that makes sense. There are not hard rules here. 
I had a look at all my redirects. An example I have - redirect from is /products/enameled-dragonfly-trinket-box, redirect to is /products/blue-green-dragonfly-trinket-box. If I want to do some tweeking (/products/trinket-box-enameled-dragonfly), I shouldn’t or are you saying by changing the “redirect to”, is ok ? Sorry, I am just struggling to get my head around it all.
Redirects are fine when you have to use them, but just make sure you have one hop. To try and simplify, imagine ABC are old/previous URLs of a product & Z is the current/new URL.
Good:
- A → Z
- B - > Z
- C → Z
Bad:
- A → B
- B → C
- C → Z
^ if someone tries to go to page A in the Bad example. Here’s what happens: 301 redirect from A to B (one hop). 301 redirect from B to C (second hop). 301 redirect from C to Z (third hop).
Three hops bad.