old deck boards - Do I need to flip/replace? or Sand? Or is it OK to re-stain as is?

Deck details: ~15yr old pressure-treated Deck in Cincinnati, OH faces west with full sun (and winter) exposure  

History: Used one-time wood ~8 yrs ago but had no maintenance since then.  

Current situation: This weekend I bought pressure washer & used Wolman Deck-Brite (powdered Oxy style product) to clean but had REALLY tough time getting off dirt/mold/etc. even with 2 applications.  Now I'm worried I may have been too aggressive w pressure washer & damaged deck boards.

My Question:  No rotting/softness of boards but I'm noting a lot of cracking & heavy splintering (perhaps on 20-30% of boards ??).  Wondering if this is normal & OK ... should I proceed with brightener & one-time woods again (I think the product worked well for me so I'm OK repeating that stain).  Or are these boards so badly damaged I need something else.  Can they be sanded down?  Or do they need to be replaced (this idea makes me sad but I don't want to invest time & $ in staining if these boards are unsalvageable).

Pics of the some splintering/cracking boards attached & also where I tried hand her belt sander but took so long ... if sanding is the next step need to step up to big tool .