It would seem that an added hardener would make SpotTone etc dye retouching and spotting more difficult (??)
I do sometimes use Formalin Hardner (be careful, is very toxic), sadly here in Portugal chrome alum is almost impossible to find, and formaldehyde is very cheap and readily available. It does add some strength to the emulsion, and wouldn't use it if I'm planning to spot, but it doesn't turn gelatin into plastic, nor makes it impossible to work on.
Also, here in Portugal, paper selection is very small, and I've always worked with I had on hand, and could afford. I do have preferences, but when I don't have the results I'm hopping for I can use reducers, toners, intensifiers to get near there. Also, I know with what I'm working with and plan my photos on that. I would trust that most papers made nowadays are of very high quality (FB or RC) and in any case, and if you do careful processing and have good preventive conservation practices, images will outlast our lives with very little or no change at all. That's just my opinion about papers, and I'm sure that there will be other opinions out there (that I do respect, and I will learn new things from them).
For me, if it allows you to work with your tools, and just doesn't turn all crazy in a few years, it's fine paper.