the high mileage motor oils have additives in them to help rejuvenate aging seals. They don't claim to bring them back from brittle, but they claim to soften and swell them a little so that the gap that are filling remains tightly filled. I do not know to what extent they actually help. The condition of seals themselves are going to be dependent on the frequency of oil change, the type of driving the car was used for, the climate and road conditions the car was driven on and in. Lots of variables. Is it a must? of course not.
Most high milage formulas come in 10w-30 weights. Since you are in a southern climate, using a 10w-30 instead of a 5w-30 will not even be noticed by your engine. 10w-30 is also an alternate weight suggested in your owners manual (at least it is in mine).
I don't really care about blends. Go one way or the other is my theory. I prefer synthetic simply due to the extreme cold that I encounter in New England winters.
50% of the oil changing world will tell you to use conventional, the other 50% will tell you to use synthetic.
There are many many threads on the subject as you already know.
The choice is up to you, and only you. You won't go wrong as long as you stick to a routine schedule of changing. Every 3000-5000 miles is what is generally suggested on most websites and by most resources. Change the filter with a qualitly filter, too. And every once in a while, if it tickles you fancy, have the oil tested to get a feel for whay the numbers look like on your engine.
steviej