I don't mind seeing TOS alumni cast members at all, but frankly now that it has been done I highly doubt we'll see Takei, Crosby, or Koenig making guest appearances on STC. If some other guest stars and/or extras get pulled out of the woodwork to appear as new characters, I'd enjoy that. Frankly enough time has passed that it's possible to do so, rather than having them appear as evolved versions of their former characters (i.e. a Captain Leslie ends up appearing in an approaching starship). It'll bring a little sentimental eye candy to the episodes without causing too much distraction.
I've also enjoyed the Phase II
episodes and it's probably best to refrain from direct comparisons given how they're crafted in different spirits. But if there's one thing I wish they'd adjust with Phase II
it's Cawley's Kirk. For me, he tries too hard to be like Shatner. There's a facial strain for emphasis that he keeps falling back on, which looks more like an impersonation rather than just personality. I know the production is Cawley's baby, and he does have quite a lot of acting experience under his belt (highly successful at being an Elvis impersonator), but he could use some coaching to polish up his Kirk persona. It would really make a pleasurable difference, given how central Kirk is to the series.