If the bearings feel choppy, or spin too freely, I would then consider replacing them. I just did the Blazer brake swap and utilized the used bearing hubs that came with my spindles. They felt pretty good as they were , but I pumped grease into the hubs and it seemed to make a big difference. They feel like new bearings. Up until they make noise or start feeling funky, I'll bite the bullet and replace them.I pulled a set of hubs as well as the spindle and calipers from a used 2001 jimmy. One of my bearings isn't as smooth as the other is hopefully a little grease inside will take care of that!
The trick grease fitting fixtures (from Riffraff Diesel) that Jared mentioned about are pretty cool. I may still consider purchasing them.