I have the opposite problem with the TOS cast as I do the TNG cast in Nemesis. In movies 3-6 the TOS cast don't look tired they look uh... way too happy to be there
. They were all fine in Wrath of Khan but after that it feels like some light-entertainment ensemble so it's hard to take the threat seriously. George Takei can't seem to hide his shit-eating grin for more than 5 seconds, Nichols always seems insanely pleased to be on camera and Doohan is stuck playing some weird comedy cartoon character.
I felt the situation in First Contact or Insurrection was serious unlike in TOS movies 3-6 where the cast gave the movies a far too friendly tone. Koenig is the only one outside the core 3 that seems to understand drama.
I'd agree Nemesis is a better film than Trek 09 (If only because Shinzon was an alright villain and Nero is the worst Trek baddie!) but I'd probably take Trek 09 over Generations. Both would be at the bottom of my movie rankings and are the films at their laziest but Trek 09 at least has the excuse of being a new cast testing the waters with the public. Generations had no excuse for being as mundane and half-arsed as it was.