I can't comment on the 50mm, but I do own the 105mm f2.8 AF-S Micro.
I'd like to suggest some points to consider on keeping/changing the 60mm
I am looking at mainly flowers to photograph
This could still make use of a wide range of focal lengths.
I find I've used the 105mm for almost as many distant subjects as close up.
BUT, its worth noting its a big & relatively heavy lens for its original intended purpose, or for that matter for walkaround. If you find Birna's review of it when it came out, you'll see he questioned this and the value of autofocus and esp VR in something he'd normally attach to a tripod and use manual focus for greater control.
If I was buying again, I'd look at a longer focal length and always liked the results of the Sigma 150mm (Nikon no longer make a Micro longer than 105 mm).
Others seem to love the 60mm micro, but I like a bigger working distance from my close-up subjects (esp insects) than this seems to allow. Of course, you could wait till the Z line has a fuller range (and probably an improved 105mm macro!)
Traditional use of the 105mm f2.8 AF-S
...and "incorrect" use (with a 1.4TC)