What's a platform?
People keep coming up with new terms. Is a platform a manufacturer? Kinda sounds like it. Got a Mossberg pump 12, and want a Remington pump 12. Got a Smith 357 revolver, and a Ruger 357 revolver.
I, personally, see no sense in that. If a gun strikes your fancy, and you can afford to buy it, get it. If it's a Smith 44, and you already have a Smith 44, who cares. Have two Smith 44s.
But buying multiple manufacturers just so you can have multiple manufacturers?
I buy because I want it. I don't worry about how much it is costing me - if I can afford to buy it - and I certainly don't worry about what it might sell for, somewhere down the line. That sounds more like someone that is investing in guns, as opposed to someone that is collecting, or accumulating guns.
If you wish to have at least two 308s, then I'd suggest a bolt for the second one. I'd even go so far as to suggest another Remington 700. Since you already have one in aught-six, you have muscle memory on how to work it. You would not need to learn how to operate a new gun.
I would not get a Henry, for a couple of reasons. First, I think they are ugly as hell. Second, I dislike their advertising. They lie. They have since they came into existence. They say they are the original Henry Rifle Company, from 1860, which is a lie. They said, when they first came out with the Big Boy, that it was SASS-legal, which was a lie. It is now, but was not then.
Look for a used 44 lever. Marlin, if you want to scope it. But get one from before Remington bought Marlin. They are better. Rossi if you want a really nice-handling gun, but get one from before Taurus bought Rossi. They are MUCH better.
What do you consider the "major manufacturers"? I have guns made by 60 different makers, from American Derringer to Zastava. I'm not sure if I've got all the "major manufacturers".