Your idea of "old" is my idea of "middle-era" - or at least those mid-to-late-90's ones are. The 70's Bantams are an aquired taste, but I enjoy them.
IMO the "good old" Trek novels come from the 80's and early 90's - Strangers From the Sky, Final Frontier, Dreadnought, Yesterday's Son, Time for Yesterday, the first two Rihannsu novels, Spock's World, The Entropy Effect, Enterprise: The First Adventure, Chain of Attack, The Final Nexus, Memory Prime, Uhura's Song, Crossroad, The Lost Years... all fantastic reads, IMO. My fondest Trek lit memories, although I do love the current post-series 24th century books too.
IMO the Shatnerverse books are just the same kind of action-heavy adventures as the recent Cold Equations trilogy. Although I must admit I have yet to re-read them (I have all the others cited above), so they may have aged poorly.