In my book, they're great even if they have the originals. I'm not much of a sentimental person. I liked the writing and organization of Labyrinth Lord better than the B/X booklets, and even though the book was heavily used, I had no regrets giving it away when I received a brand new copy of the Old School Essentials book last year. It's all the same rules, but cleaner, better looking, with less worn pages. It's like buying a new lawnmower every ten years.
If you liked Star Frontiers, FrontierSpace is a love letter to the game. The rules are different, still percentile, but less fiddly, the square grid is replaced by hexes (and there's no board and chits in the book), but the feel is the same.
Thousand Suns has a similar story - it's Classic Traveller, with improved mechanical chassis. The 2d6 core has been replaced by a 2d12 system operating on the same basis, but with more granularity. The game has no setting, but an implied metasetting - a set of assumptions about the setting that it makes and that should be true. Of course, those requirements are satisfied by Traveller's Third Imperium, so you can use it as an engine to power Traveller campaigns. There are little bits about this one that I adore, like the book being full of classical quotes, from Asimov, Bester, Doc Smith. And the fact that Esperanto is the language of the empire.
That little OD&D Barsoom booklet is a thing of beauty. Same goes for Jason Vey's Age of Conan. The abstract nature of OD&D fits well with pulp sensibilities.