In thinking about it, I think you're right. Tuvok did seem to be more cynical than Spock. That is a pretty good difference between the two. I seem to recall an episode where Tuvok was discussing Spock's politics with Janeway (was it regarding the Klingons?), and I think he mentioned that he initially disagreed with him. It seemed that Tuvok and Valeris had similar views of the Klingons. Would Tuvok have entered her conspiracy if he'd gotten the opportunity? Man, that could've been a hell of a flashback episode!
That would have made for some interesting drama. Unlike Valeris though, Tuvok could be talked into Spock's way of thinking which shows he was a bit more flexible.
It's a real shame, Chakotay's best scenes (in the end, his only good ones) were discussing strategy with Janeway. I always wondered why if Tuvok is an old friend, a Vulcan, and her third officer, why he wasn't privy to those discussions as well. I always thought that was kind of a slap in the face to Tuvok. They touched on Chakotay believing that Tuvok resented him and Tuvok denying it. They could've done a lot more with that Janeway-Chakotay-Tuvok interplay than they did, which was virtually nothing. If they had, Chakotay and Tuvok would've come out as better characters (especially Chakotay).
Well the relationship between J & C is a complex one in itself but yes you have to wonder how it affected the friendship between Tuvok and Janeway.