Hi Horms57,
First of all I have to congratulate you on what has clearly been some great research. None of our final choices have any “weak links” and in terms of quality and value they are all certainly good choices. You have clearly taken the information here to heart and used it very effectively.
When you are down to final choices between what I would consider “all good options” (and they are) then “value” to me is really a matter of all the objective, subjective, and even intangible factors that are the most important parts of your personal value equation besides just the “commodity value” of the mattress. I look at all the parts of the entire purchase not just the materials in the mattress. This of course would include which of them provided the best PPP (Pressure relief, Posture and alignment, and Personal preferences), which have the best options or “extras” that are part of the purchase, and all the other things that may be important to you including how I feel about dealing with the retailer or manufacturer I am dealing with and their service before, during, and after the sale. When you are looking at options like this as well it may also be worthwhile to let each one know that you are down to three that are all good value and is there anything they can offer that would “help you make your choice”.
So I can’t really say which one I would choose except by sharing what I would be considering and looking at based on my own preferences and thought processes because any of these would make a good choice IMO.
My own choices would probably lean towards either the Opulence or the Dreamline so in my case the first one I would exclude is the Grandeur because it is an “in the middle choice” that would not be as attractive to me as the other two.
My overall sense is that the Dreamline has slightly better “commodity value” but since they are all good value this would not be my main consideration
Having said that … there would also be an real attraction to spending $900 less even though in “value” terms they are much closer than that (latex is a more costly material)
My personal preferences (which may be completely different from the preferences of other people) normally leans towards all latex (which is what I sleep on) which would mean that I would normally lean towards the Opulence but having said that, one of my favorite hybrid constructions is also a thinner layer of latex over a relatively thin layer of memory foam which I also like very much. The top layer of latex provides a more resilient surface and the memory foam underneath it has a slow sinking feeling that is initially firmer and then softens gradually that I also really like.
All materials will also get softer over time but 5.25 lb memory foam is a very durable material … particularly under latex … and durability or softening beyond the initial break in period of the mattress wouldn’t be an issue for me.
I think that if it was me I would spend about 30 minutes (and I know that’s a long time) lying on the Dreamline because it has thicker layers of relatively soft foam on top (even though the memory foam may be firmer initially) and I would want to make sure that my alignment was good after the memory foam had a little longer to warm up and soften with body heat. Since you are a side sleeper this would be less of a concern than it would with back or stomach sleeping but with the memory foam a little deeper in the mattress I would want to make sure that the mattress wasn’t too soft for good alignment over a longer period of time. I don’t know the firmness of the convoluted foam so this could either be more of a firmer transition layer or a softer layer but again I would trust my testing. The latex mattress has a softer comfort layer or “pressure relief softness” but there is more to sink into in the Dreamline so it would probably have more “support softness” over the course of the night (you can see more about the different types of softness here).
If everything tested out well … I think I would make my choice based on my “gut feel” and on which one had the “ahhh” factor of being able to totally relax on the mattress where everything seemed more “right” and that just seemed more “inviting”.
In “value” terms … I would probably give a slight edge to the Dreamline and the significantly lower cost would also have its attraction as well but years down the road you will remember much more about how well you slept than what you paid for the mattress (either way) so I would make my final choice heavily weighted towards which one was most attractive based on PPP and any other factors that were important rather than just price alone (assuming they are both comfortably in your budget).
So after all this hemming and hawing I guess what I’m trying to say is that I would need to lie on each mattress and go through the experience of dealing with each retailer to make a final choice because I wouldn’t hesitate to buy either of them for different reasons.
You really have done well because the best place to be in is when the final choices are very difficult because they are all good ones and outside of"suitability" (which only you can know) I don’t think you would be making a mistake with any of these in terms of quality or value 
Phoenix