You may have to not only clean it but etch it so you have a fairly uniform starting color. Then stain it and maybe acid etch it again for color effect. Then seal it with something that has some tooth to it so you are not slipping around when it is wet.
You might look online for staining ideas and think about a varigated approach rather than trying to achieve a solid color change. Seems a shame to waste all those kegs to Beer Stain it! Seriously, there are many brands of concrete stains out there. You might check with your local concrete supplier to see what products they recommend. The Beer Stain looked to have a fair amount of UV protection in it which is certainly a good idea.
The decking does look to be in decent shape so overall I would say staining, acid ethching or whatever seems a reasonable way to bring it back to life.
Be careful not to go with so dark a color you cannot stand to walk on it when it gets hot!
Repair and fill your expansion joints while you are at this?