I guess I'll be the lone dissenter here.
To me, those old kits (T55 and BMPs) are not worth the effort to bring up to modern standards of detail. I would rather buy a more modern kit. Tamiya's T55 is really nice and Trumpeter's BMPs are very nice as well. Additionally, if you end up buying a bunch of AM resin and PE to add to them to correct or bring up the level of detail, you end up spending more than a modern, updated kit of the same subjects.
The only thing they would be even remotely good for to me is to make a burned-out hulk out of. Even then, I would still rather start with a more detailed, updated kit.